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 $64.57   3.291%   $66.695   $66.70   $66.70   $66.70  
  Purchase #2 $185.78   5.471%   $195.944   $195.94   $195.95   $195.90  
  Purchase #3 $239.88   4.866%   $251.5526   $251.55   $251.55   $251.60  
  Purchase #4 $51.41   10.396%   $56.7546   $56.75   $56.75   $56.80  
  Purchase #5 $29.75   8.740%   $32.3502   $32.35   $32.35   $32.40  
  Purchase #6 $155.50   5.839%   $164.5796   $164.58   $164.60   $164.60  
  Purchase #7 $213.33   8.813%   $232.1308   $232.13   $232.15   $232.10  
  7 purchase totals = $940.22       $1,000.0068   $1,000.00   $1,000.05   $1,000.10