Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $32.47   4.537%   $33.9432   $33.94   $33.95   $33.90  
  Purchase #2 $169.87   9.667%   $186.2913   $186.29   $186.30   $186.30  
  Purchase #3 $145.80   13.449%   $165.4086   $165.41   $165.40   $165.40  
  Purchase #4 $187.61   11.420%   $209.0351   $209.04   $209.05   $209.00  
  Purchase #5 $198.31   8.788%   $215.7375   $215.74   $215.75   $215.70  
  Purchase #6 $159.32   11.755%   $178.0481   $178.05   $178.05   $178.00  
  Purchase #7 $163.75   12.570%   $184.3334   $184.33   $184.35   $184.30  
  7 purchase totals = $1,057.13       $1,172.7972   $1,172.80   $1,172.85   $1,172.60