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 $55.40   6.681%   $59.1013   $59.10   $59.10   $59.10  
  Purchase #2 $125.72   12.118%   $140.9547   $140.95   $140.95   $141.00  
  Purchase #3 $233.67   12.867%   $263.7363   $263.74   $263.75   $263.70  
  Purchase #4 $25.97   4.625%   $27.1711   $27.17   $27.15   $27.20  
  Purchase #5 $108.34   7.776%   $116.7645   $116.76   $116.75   $116.80  
  Purchase #6 $210.85   13.769%   $239.8819   $239.88   $239.90   $239.90  
  Purchase #7 $49.74   7.247%   $53.3447   $53.34   $53.35   $53.30  
  7 purchase totals = $809.69       $900.9545   $900.94   $900.95   $901.00