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 $66.93   13.307%   $75.8364   $75.84   $75.85   $75.80  
  Purchase #2 $216.33   10.405%   $238.8391   $238.84   $238.85   $238.80  
  Purchase #3 $236.35   8.149%   $255.6102   $255.61   $255.60   $255.60  
  Purchase #4 $183.64   7.828%   $198.0153   $198.02   $198.00   $198.00  
  Purchase #5 $249.86   5.359%   $263.25   $263.25   $263.25   $263.30  
  Purchase #6 $223.46   10.545%   $247.0239   $247.02   $247.00   $247.00  
  Purchase #7 $239.97   6.190%   $254.8241   $254.82   $254.80   $254.80  
  7 purchase totals = $1,416.54       $1,533.3990   $1,533.40   $1,533.35   $1,533.30