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 $60.76   9.452%   $66.503   $66.50   $66.50   $66.50  
  Purchase #2 $188.94   7.699%   $203.4865   $203.49   $203.50   $203.50  
  Purchase #3 $53.53   3.688%   $55.5042   $55.50   $55.50   $55.50  
  Purchase #4 $230.60   4.498%   $240.9724   $240.97   $240.95   $241.00  
  Purchase #5 $30.91   11.610%   $34.4987   $34.50   $34.50   $34.50  
  Purchase #6 $223.59   5.549%   $235.997   $236.00   $236.00   $236.00  
  Purchase #7 $191.79   13.326%   $217.3479   $217.35   $217.35   $217.30  
  7 purchase totals = $980.12       $1,054.3097   $1,054.31   $1,054.30   $1,054.30