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 $70.89   4.216%   $73.8787   $73.88   $73.90   $73.90  
  Purchase #2 $119.31   9.207%   $130.2949   $130.29   $130.30   $130.30  
  Purchase #3 $117.72   5.479%   $124.1699   $124.17   $124.15   $124.20  
  Purchase #4 $209.55   13.127%   $237.0576   $237.06   $237.05   $237.10  
  Purchase #5 $74.50   11.804%   $83.294   $83.29   $83.30   $83.30  
  Purchase #6 $201.55   12.107%   $225.9517   $225.95   $225.95   $226.00  
  Purchase #7 $187.34   5.274%   $197.2203   $197.22   $197.20   $197.20  
  7 purchase totals = $980.86       $1,071.8671   $1,071.86   $1,071.85   $1,072.00