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 $216.84   13.536%   $246.1915   $246.19   $246.20   $246.20  
  Purchase #2 $126.98   6.210%   $134.8655   $134.87   $134.85   $134.90  
  Purchase #3 $117.59   10.532%   $129.9746   $129.97   $129.95   $130.00  
  Purchase #4 $238.49   6.751%   $254.5905   $254.59   $254.60   $254.60  
  Purchase #5 $185.67   13.338%   $210.4347   $210.43   $210.45   $210.40  
  Purchase #6 $144.83   13.406%   $164.2459   $164.25   $164.25   $164.20  
  Purchase #7 $98.53   8.351%   $106.7582   $106.76   $106.75   $106.80  
  7 purchase totals = $1,128.93       $1,247.0609   $1,247.06   $1,247.05   $1,247.10