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 $188.85   9.597%   $206.9739   $206.97   $206.95   $207.00  
  Purchase #2 $244.36   10.763%   $270.6605   $270.66   $270.65   $270.70  
  Purchase #3 $17.30   13.610%   $19.6545   $19.65   $19.65   $19.70  
  Purchase #4 $84.60   9.595%   $92.7174   $92.72   $92.70   $92.70  
  Purchase #5 $69.55   11.855%   $77.7952   $77.80   $77.80   $77.80  
  Purchase #6 $7.95   3.325%   $8.2143   $8.21   $8.20   $8.20  
  Purchase #7 $247.57   7.638%   $266.4794   $266.48   $266.50   $266.50  
  7 purchase totals = $860.18       $942.4952   $942.49   $942.45   $942.60