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 $65.50   8.316%   $70.947   $70.95   $70.95   $70.90  
  Purchase #2 $63.67   9.518%   $69.7301   $69.73   $69.75   $69.70  
  Purchase #3 $73.36   7.703%   $79.0109   $79.01   $79.00   $79.00  
  Purchase #4 $87.32   4.607%   $91.3428   $91.34   $91.35   $91.30  
  Purchase #5 $118.61   11.375%   $132.1019   $132.10   $132.10   $132.10  
  Purchase #6 $74.42   8.817%   $80.9816   $80.98   $81.00   $81.00  
  Purchase #7 $170.73   4.214%   $177.9246   $177.92   $177.90   $177.90  
  7 purchase totals = $653.61       $702.0389   $702.03   $702.05   $701.90