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 $61.96   10.812%   $68.6591   $68.66   $68.65   $68.70  
  Purchase #2 $109.70   8.414%   $118.9302   $118.93   $118.95   $118.90  
  Purchase #3 $199.73   7.424%   $214.558   $214.56   $214.55   $214.60  
  Purchase #4 $90.49   11.790%   $101.1588   $101.16   $101.15   $101.20  
  Purchase #5 $134.95   6.566%   $143.8108   $143.81   $143.80   $143.80  
  Purchase #6 $9.37   10.714%   $10.3739   $10.37   $10.35   $10.40  
  Purchase #7 $244.92   9.630%   $268.5058   $268.51   $268.50   $268.50  
  7 purchase totals = $851.12       $925.9966   $926.00   $925.95   $926.10