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 $206.27   3.235%   $212.9428   $212.94   $212.95   $212.90  
  Purchase #2 $224.76   5.724%   $237.6253   $237.63   $237.65   $237.60  
  Purchase #3 $50.75   6.104%   $53.8478   $53.85   $53.85   $53.80  
  Purchase #4 $210.43   6.661%   $224.4467   $224.45   $224.45   $224.40  
  Purchase #5 $113.50   11.561%   $126.6217   $126.62   $126.60   $126.60  
  Purchase #6 $237.79   11.310%   $264.684   $264.68   $264.70   $264.70  
  Purchase #7 $177.97   12.331%   $199.9155   $199.92   $199.90   $199.90  
  7 purchase totals = $1,221.47       $1,320.0838   $1,320.09   $1,320.10   $1,319.90