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 $61.58   8.555%   $66.8482   $66.85   $66.85   $66.80  
  Purchase #2 $205.67   3.621%   $213.1173   $213.12   $213.10   $213.10  
  Purchase #3 $202.58   7.354%   $217.4777   $217.48   $217.50   $217.50  
  Purchase #4 $8.82   11.816%   $9.8622   $9.86   $9.85   $9.90  
  Purchase #5 $138.73   8.833%   $150.984   $150.98   $151.00   $151.00  
  Purchase #6 $61.28   7.543%   $65.9024   $65.90   $65.90   $65.90  
  Purchase #7 $229.82   7.587%   $247.2564   $247.26   $247.25   $247.30  
  7 purchase totals = $908.48       $971.4482   $971.45   $971.45   $971.50