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 $39.67   12.142%   $44.4867   $44.49   $44.50   $44.50  
  Purchase #2 $217.26   4.767%   $227.6168   $227.62   $227.60   $227.60  
  Purchase #3 $141.26   8.391%   $153.1131   $153.11   $153.10   $153.10  
  Purchase #4 $97.94   13.621%   $111.2804   $111.28   $111.30   $111.30  
  Purchase #5 $124.86   4.567%   $130.5624   $130.56   $130.55   $130.60  
  Purchase #6 $67.95   6.408%   $72.3042   $72.30   $72.30   $72.30  
  Purchase #7 $192.66   13.652%   $218.9619   $218.96   $218.95   $219.00  
  7 purchase totals = $881.60       $958.3255   $958.32   $958.30   $958.40