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 $218.82   12.425%   $246.0084   $246.01   $246.00   $246.00  
  Purchase #2 $205.72   9.608%   $225.4856   $225.49   $225.50   $225.50  
  Purchase #3 $35.60   7.378%   $38.2266   $38.23   $38.25   $38.20  
  Purchase #4 $244.73   7.862%   $263.9707   $263.97   $263.95   $264.00  
  Purchase #5 $237.89   8.801%   $258.8267   $258.83   $258.85   $258.80  
  Purchase #6 $95.81   10.189%   $105.5721   $105.57   $105.55   $105.60  
  Purchase #7 $69.79   7.781%   $75.2204   $75.22   $75.20   $75.20  
  7 purchase totals = $1,108.36       $1,213.3105   $1,213.32   $1,213.30   $1,213.30