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 $55.75   5.505%   $58.819   $58.82   $58.80   $58.80  
  Purchase #2 $77.87   12.452%   $87.5664   $87.57   $87.55   $87.60  
  Purchase #3 $10.56   8.261%   $11.4324   $11.43   $11.45   $11.40  
  Purchase #4 $153.87   13.526%   $174.6825   $174.68   $174.70   $174.70  
  Purchase #5 $51.42   7.419%   $55.2348   $55.23   $55.25   $55.20  
  Purchase #6 $246.27   3.393%   $254.6259   $254.63   $254.65   $254.60  
  Purchase #7 $113.63   7.681%   $122.3579   $122.36   $122.35   $122.40  
  7 purchase totals = $709.37       $764.7189   $764.72   $764.75   $764.70