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 $49.79   8.497%   $54.0207   $54.02   $54.00   $54.00  
  Purchase #2 $208.88   6.255%   $221.9454   $221.95   $221.95   $221.90  
  Purchase #3 $188.74   4.872%   $197.9354   $197.94   $197.95   $197.90  
  Purchase #4 $245.50   5.542%   $259.1056   $259.11   $259.10   $259.10  
  Purchase #5 $22.76   9.210%   $24.8562   $24.86   $24.85   $24.90  
  Purchase #6 $247.93   8.823%   $269.8049   $269.80   $269.80   $269.80  
  Purchase #7 $19.39   8.200%   $20.98   $20.98   $21.00   $21.00  
  7 purchase totals = $982.99       $1,048.6482   $1,048.66   $1,048.65   $1,048.60