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 $84.31   9.137%   $92.0134   $92.01   $92.00   $92.00  
  Purchase #2 $60.37   10.457%   $66.6829   $66.68   $66.70   $66.70  
  Purchase #3 $103.77   4.790%   $108.7406   $108.74   $108.75   $108.70  
  Purchase #4 $116.39   12.311%   $130.7188   $130.72   $130.70   $130.70  
  Purchase #5 $62.79   3.335%   $64.884   $64.88   $64.90   $64.90  
  Purchase #6 $247.84   6.491%   $263.9273   $263.93   $263.95   $263.90  
  Purchase #7 $25.55   8.786%   $27.7948   $27.79   $27.80   $27.80  
  7 purchase totals = $701.02       $754.7618   $754.75   $754.80   $754.70