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 $76.64   13.453%   $86.9504   $86.95   $86.95   $87.00  
  Purchase #2 $57.50   12.763%   $64.8387   $64.84   $64.85   $64.80  
  Purchase #3 $223.47   11.549%   $249.2786   $249.28   $249.30   $249.30  
  Purchase #4 $168.98   4.115%   $175.9335   $175.93   $175.95   $175.90  
  Purchase #5 $49.73   8.288%   $53.8516   $53.85   $53.85   $53.90  
  Purchase #6 $91.31   5.684%   $96.5001   $96.50   $96.50   $96.50  
  Purchase #7 $69.92   6.562%   $74.5082   $74.51   $74.50   $74.50  
  7 purchase totals = $737.55       $801.8611   $801.86   $801.90   $801.90