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 $231.61   12.126%   $259.695   $259.70   $259.70   $259.70  
  Purchase #2 $150.35   13.634%   $170.8487   $170.85   $170.85   $170.80  
  Purchase #3 $48.47   11.747%   $54.1638   $54.16   $54.15   $54.20  
  Purchase #4 $66.90   3.827%   $69.4603   $69.46   $69.45   $69.50  
  Purchase #5 $210.42   11.690%   $235.0181   $235.02   $235.00   $235.00  
  Purchase #6 $110.65   11.531%   $123.4091   $123.41   $123.40   $123.40  
  Purchase #7 $124.66   7.202%   $133.638   $133.64   $133.65   $133.60  
  7 purchase totals = $943.06       $1,046.2330   $1,046.24   $1,046.20   $1,046.20