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 $95.93   3.166%   $98.9671   $98.97   $98.95   $99.00  
  Purchase #2 $15.65   10.319%   $17.2649   $17.26   $17.25   $17.30  
  Purchase #3 $182.91   5.518%   $193.003   $193.00   $193.00   $193.00  
  Purchase #4 $133.52   11.329%   $148.6465   $148.65   $148.65   $148.60  
  Purchase #5 $10.51   12.363%   $11.8094   $11.81   $11.80   $11.80  
  Purchase #6 $70.33   5.414%   $74.1377   $74.14   $74.15   $74.10  
  Purchase #7 $44.69   5.334%   $47.0738   $47.07   $47.05   $47.10  
  7 purchase totals = $553.54       $590.9024   $590.90   $590.85   $590.90