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 $88.55   6.352%   $94.1747   $94.17   $94.15   $94.20  
  Purchase #2 $239.91   13.190%   $271.5541   $271.55   $271.55   $271.60  
  Purchase #3 $242.51   6.608%   $258.5351   $258.54   $258.55   $258.50  
  Purchase #4 $224.95   4.628%   $235.3607   $235.36   $235.35   $235.40  
  Purchase #5 $101.55   6.509%   $108.1599   $108.16   $108.15   $108.20  
  Purchase #6 $231.68   9.591%   $253.9004   $253.90   $253.90   $253.90  
  Purchase #7 $55.75   7.653%   $60.0165   $60.02   $60.00   $60.00  
  7 purchase totals = $1,184.90       $1,281.7014   $1,281.70   $1,281.65   $1,281.80