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 $43.69   9.829%   $47.9843   $47.98   $48.00   $48.00  
  Purchase #2 $20.66   3.312%   $21.3443   $21.34   $21.35   $21.30  
  Purchase #3 $177.33   13.795%   $201.7927   $201.79   $201.80   $201.80  
  Purchase #4 $248.57   4.265%   $259.1715   $259.17   $259.15   $259.20  
  Purchase #5 $63.31   6.259%   $67.2726   $67.27   $67.25   $67.30  
  Purchase #6 $207.82   10.779%   $230.2209   $230.22   $230.20   $230.20  
  Purchase #7 $122.70   8.718%   $133.397   $133.40   $133.40   $133.40  
  7 purchase totals = $884.08       $961.1833   $961.17   $961.15   $961.20