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 $197.79   10.732%   $219.0168   $219.02   $219.00   $219.00  
  Purchase #2 $54.66   7.264%   $58.6305   $58.63   $58.65   $58.60  
  Purchase #3 $234.51   5.224%   $246.7608   $246.76   $246.75   $246.80  
  Purchase #4 $206.34   8.851%   $224.6032   $224.60   $224.60   $224.60  
  Purchase #5 $245.71   5.371%   $258.9071   $258.91   $258.90   $258.90  
  Purchase #6 $50.55   7.604%   $54.3938   $54.39   $54.40   $54.40  
  Purchase #7 $123.94   3.414%   $128.1713   $128.17   $128.15   $128.20  
  7 purchase totals = $1,113.50       $1,190.4835   $1,190.48   $1,190.45   $1,190.50