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 $89.44   3.679%   $92.7305   $92.73   $92.75   $92.70  
  Purchase #2 $158.60   12.593%   $178.5725   $178.57   $178.55   $178.60  
  Purchase #3 $186.55   7.520%   $200.5786   $200.58   $200.60   $200.60  
  Purchase #4 $54.62   13.444%   $61.9631   $61.96   $61.95   $62.00  
  Purchase #5 $92.56   6.354%   $98.4413   $98.44   $98.45   $98.40  
  Purchase #6 $88.59   10.591%   $97.9726   $97.97   $97.95   $98.00  
  Purchase #7 $240.98   9.219%   $263.1959   $263.20   $263.20   $263.20  
  7 purchase totals = $911.34       $993.4545   $993.45   $993.45   $993.50