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 $86.84   8.163%   $93.9287   $93.93   $93.95   $93.90  
  Purchase #2 $107.44   12.470%   $120.8378   $120.84   $120.85   $120.80  
  Purchase #3 $65.35   4.355%   $68.196   $68.20   $68.20   $68.20  
  Purchase #4 $125.51   11.173%   $139.5332   $139.53   $139.55   $139.50  
  Purchase #5 $85.73   5.473%   $90.422   $90.42   $90.40   $90.40  
  Purchase #6 $168.74   9.248%   $184.3451   $184.35   $184.35   $184.30  
  Purchase #7 $242.73   9.720%   $266.3234   $266.32   $266.30   $266.30  
  7 purchase totals = $882.34       $963.5862   $963.59   $963.60   $963.40