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 $117.35   5.218%   $123.4733   $123.47   $123.45   $123.50  
  Purchase #2 $67.66   3.809%   $70.2372   $70.24   $70.25   $70.20  
  Purchase #3 $69.58   13.279%   $78.8195   $78.82   $78.80   $78.80  
  Purchase #4 $215.29   9.229%   $235.1591   $235.16   $235.15   $235.20  
  Purchase #5 $58.27   12.870%   $65.7693   $65.77   $65.75   $65.80  
  Purchase #6 $173.58   11.764%   $194   $194.00   $194.00   $194.00  
  Purchase #7 $84.87   12.568%   $95.5365   $95.54   $95.55   $95.50  
  7 purchase totals = $786.60       $862.9949   $863.00   $862.95   $863.00