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 $102.83   7.853%   $110.9052   $110.91   $110.90   $110.90  
  Purchase #2 $107.60   9.338%   $117.6477   $117.65   $117.65   $117.60  
  Purchase #3 $132.53   9.673%   $145.3496   $145.35   $145.35   $145.30  
  Purchase #4 $69.30   12.777%   $78.1545   $78.15   $78.15   $78.20  
  Purchase #5 $28.59   9.518%   $31.3112   $31.31   $31.30   $31.30  
  Purchase #6 $39.81   13.351%   $45.125   $45.13   $45.15   $45.10  
  Purchase #7 $7.47   9.188%   $8.1563   $8.16   $8.15   $8.20  
  7 purchase totals = $488.13       $536.6495   $536.66   $536.65   $536.60