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 $83.99   12.182%   $94.2217   $94.22   $94.20   $94.20  
  Purchase #2 $155.31   7.279%   $166.615   $166.62   $166.60   $166.60  
  Purchase #3 $241.89   9.399%   $264.6252   $264.63   $264.65   $264.60  
  Purchase #4 $98.42   10.365%   $108.6212   $108.62   $108.60   $108.60  
  Purchase #5 $204.83   6.812%   $218.783   $218.78   $218.80   $218.80  
  Purchase #6 $167.98   8.491%   $182.2432   $182.24   $182.25   $182.20  
  Purchase #7 $61.26   4.464%   $63.9946   $63.99   $64.00   $64.00  
  7 purchase totals = $1,013.68       $1,099.1039   $1,099.10   $1,099.10   $1,099.00