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 $33.71   8.342%   $36.5221   $36.52   $36.50   $36.50  
  Purchase #2 $215.84   13.723%   $245.4597   $245.46   $245.45   $245.50  
  Purchase #3 $25.28   5.718%   $26.7255   $26.73   $26.75   $26.70  
  Purchase #4 $55.92   9.514%   $61.2402   $61.24   $61.25   $61.20  
  Purchase #5 $102.54   12.670%   $115.5318   $115.53   $115.55   $115.50  
  Purchase #6 $118.32   4.688%   $123.8668   $123.87   $123.85   $123.90  
  Purchase #7 $165.47   5.375%   $174.364   $174.36   $174.35   $174.40  
  7 purchase totals = $717.08       $783.7101   $783.71   $783.70   $783.70