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 $56.57   12.761%   $63.7889   $63.79   $63.80   $63.80  
  Purchase #2 $221.63   9.281%   $242.1995   $242.20   $242.20   $242.20  
  Purchase #3 $216.51   6.442%   $230.4576   $230.46   $230.45   $230.50  
  Purchase #4 $69.37   6.152%   $73.6376   $73.64   $73.65   $73.60  
  Purchase #5 $134.83   8.740%   $146.6141   $146.61   $146.60   $146.60  
  Purchase #6 $88.63   5.109%   $93.1581   $93.16   $93.15   $93.20  
  Purchase #7 $72.50   4.227%   $75.5646   $75.56   $75.55   $75.60  
  7 purchase totals = $860.04       $925.4204   $925.42   $925.40   $925.50