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 $41.97   6.268%   $44.6007   $44.60   $44.60   $44.60  
  Purchase #2 $94.85   12.511%   $106.7167   $106.72   $106.70   $106.70  
  Purchase #3 $170.49   11.644%   $190.3419   $190.34   $190.35   $190.30  
  Purchase #4 $42.70   7.711%   $45.9926   $45.99   $46.00   $46.00  
  Purchase #5 $241.90   13.775%   $275.2217   $275.22   $275.20   $275.20  
  Purchase #6 $97.40   6.119%   $103.3599   $103.36   $103.35   $103.40  
  Purchase #7 $32.87   8.124%   $35.5404   $35.54   $35.55   $35.50  
  7 purchase totals = $722.18       $801.7739   $801.77   $801.75   $801.70