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 $152.96   13.534%   $173.6616   $173.66   $173.65   $173.70  
  Purchase #2 $14.35   10.229%   $15.8179   $15.82   $15.80   $15.80  
  Purchase #3 $125.64   3.170%   $129.6228   $129.62   $129.60   $129.60  
  Purchase #4 $119.76   10.633%   $132.4941   $132.49   $132.50   $132.50  
  Purchase #5 $240.26   10.215%   $264.8026   $264.80   $264.80   $264.80  
  Purchase #6 $70.61   5.288%   $74.3439   $74.34   $74.35   $74.30  
  Purchase #7 $140.78   6.766%   $150.3052   $150.31   $150.30   $150.30  
  7 purchase totals = $864.36       $941.0481   $941.04   $941.00   $941.00