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 $67.27   6.592%   $71.7044   $71.70   $71.70   $71.70  
  Purchase #2 $93.42   9.104%   $101.925   $101.93   $101.95   $101.90  
  Purchase #3 $191.71   11.457%   $213.6742   $213.67   $213.65   $213.70  
  Purchase #4 $129.62   8.447%   $140.569   $140.57   $140.55   $140.60  
  Purchase #5 $62.82   4.792%   $65.8303   $65.83   $65.85   $65.80  
  Purchase #6 $239.40   4.637%   $250.501   $250.50   $250.50   $250.50  
  Purchase #7 $9.93   8.512%   $10.7752   $10.78   $10.80   $10.80  
  7 purchase totals = $794.17       $854.9791   $854.98   $855.00   $855.00