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 $59.88   9.212%   $65.3961   $65.40   $65.40   $65.40  
  Purchase #2 $123.66   12.662%   $139.3178   $139.32   $139.30   $139.30  
  Purchase #3 $240.38   13.259%   $272.252   $272.25   $272.25   $272.30  
  Purchase #4 $60.32   3.580%   $62.4795   $62.48   $62.50   $62.50  
  Purchase #5 $9.41   10.557%   $10.4034   $10.40   $10.40   $10.40  
  Purchase #6 $130.49   8.296%   $141.3155   $141.32   $141.30   $141.30  
  Purchase #7 $106.53   10.409%   $117.6187   $117.62   $117.60   $117.60  
  7 purchase totals = $730.67       $808.7830   $808.79   $808.75   $808.80