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 $84.48   12.859%   $95.3433   $95.34   $95.35   $95.30  
  Purchase #2 $121.57   3.266%   $125.5405   $125.54   $125.55   $125.50  
  Purchase #3 $90.97   3.330%   $93.9993   $94.00   $94.00   $94.00  
  Purchase #4 $154.65   4.826%   $162.1134   $162.11   $162.10   $162.10  
  Purchase #5 $209.93   11.833%   $234.771   $234.77   $234.75   $234.80  
  Purchase #6 $42.65   3.554%   $44.1658   $44.17   $44.15   $44.20  
  Purchase #7 $211.93   5.529%   $223.6476   $223.65   $223.65   $223.60  
  7 purchase totals = $916.18       $979.5809   $979.58   $979.55   $979.50