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 $88.87   6.618%   $94.7514   $94.75   $94.75   $94.80  
  Purchase #2 $213.60   13.126%   $241.6371   $241.64   $241.65   $241.60  
  Purchase #3 $173.75   11.807%   $194.2647   $194.26   $194.25   $194.30  
  Purchase #4 $193.89   9.108%   $211.5495   $211.55   $211.55   $211.50  
  Purchase #5 $79.26   12.572%   $89.2246   $89.22   $89.20   $89.20  
  Purchase #6 $136.61   8.714%   $148.5142   $148.51   $148.50   $148.50  
  Purchase #7 $71.42   3.207%   $73.7104   $73.71   $73.70   $73.70  
  7 purchase totals = $957.40       $1,053.6519   $1,053.64   $1,053.60   $1,053.60