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 $60.39   3.799%   $62.6842   $62.68   $62.70   $62.70  
  Purchase #2 $203.66   4.379%   $212.5783   $212.58   $212.60   $212.60  
  Purchase #3 $204.69   13.464%   $232.2495   $232.25   $232.25   $232.20  
  Purchase #4 $46.95   5.450%   $49.5088   $49.51   $49.50   $49.50  
  Purchase #5 $193.48   4.685%   $202.5445   $202.54   $202.55   $202.50  
  Purchase #6 $6.86   8.339%   $7.4321   $7.43   $7.45   $7.40  
  Purchase #7 $46.62   11.126%   $51.8069   $51.81   $51.80   $51.80  
  7 purchase totals = $762.65       $818.8043   $818.80   $818.85   $818.70