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 $184.66   6.382%   $196.445   $196.45   $196.45   $196.40  
  Purchase #2 $110.55   11.453%   $123.2113   $123.21   $123.20   $123.20  
  Purchase #3 $242.42   5.481%   $255.707   $255.71   $255.70   $255.70  
  Purchase #4 $111.68   8.271%   $120.9171   $120.92   $120.90   $120.90  
  Purchase #5 $91.66   10.808%   $101.5666   $101.57   $101.55   $101.60  
  Purchase #6 $36.52   6.569%   $38.919   $38.92   $38.90   $38.90  
  Purchase #7 $23.79   12.155%   $26.6817   $26.68   $26.70   $26.70  
  7 purchase totals = $801.28       $863.4477   $863.46   $863.40   $863.40