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 $7.40   9.595%   $8.11   $8.11   $8.10   $8.10  
  Purchase #2 $171.46   5.398%   $180.7154   $180.72   $180.70   $180.70  
  Purchase #3 $175.59   6.624%   $187.2211   $187.22   $187.20   $187.20  
  Purchase #4 $108.30   12.786%   $122.1472   $122.15   $122.15   $122.10  
  Purchase #5 $132.66   3.329%   $137.0763   $137.08   $137.10   $137.10  
  Purchase #6 $85.60   13.454%   $97.1166   $97.12   $97.10   $97.10  
  Purchase #7 $87.59   13.327%   $99.2631   $99.26   $99.25   $99.30  
  7 purchase totals = $768.60       $831.6497   $831.66   $831.60   $831.60