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 $113.37   4.261%   $118.2007   $118.20   $118.20   $118.20  
  Purchase #2 $110.79   12.199%   $124.3053   $124.31   $124.30   $124.30  
  Purchase #3 $244.79   6.423%   $260.5129   $260.51   $260.50   $260.50  
  Purchase #4 $82.87   11.676%   $92.5459   $92.55   $92.55   $92.50  
  Purchase #5 $37.26   6.790%   $39.79   $39.79   $39.80   $39.80  
  Purchase #6 $217.29   3.812%   $225.5731   $225.57   $225.55   $225.60  
  Purchase #7 $53.74   7.150%   $57.5824   $57.58   $57.60   $57.60  
  7 purchase totals = $860.11       $918.5103   $918.51   $918.50   $918.50