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 $82.58   12.311%   $92.7464   $92.75   $92.75   $92.70  
  Purchase #2 $87.44   11.687%   $97.6591   $97.66   $97.65   $97.70  
  Purchase #3 $24.46   7.287%   $26.2424   $26.24   $26.25   $26.20  
  Purchase #4 $177.35   4.154%   $184.7171   $184.72   $184.70   $184.70  
  Purchase #5 $248.50   12.856%   $280.4472   $280.45   $280.45   $280.40  
  Purchase #6 $54.84   5.456%   $57.8321   $57.83   $57.85   $57.80  
  Purchase #7 $226.36   9.347%   $247.5179   $247.52   $247.50   $247.50  
  7 purchase totals = $901.53       $987.1622   $987.17   $987.15   $987.00