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 $14.84   8.212%   $16.0587   $16.06   $16.05   $16.10  
  Purchase #2 $148.40   12.307%   $166.6636   $166.66   $166.65   $166.70  
  Purchase #3 $135.98   7.331%   $145.9487   $145.95   $145.95   $145.90  
  Purchase #4 $87.93   11.152%   $97.736   $97.74   $97.75   $97.70  
  Purchase #5 $28.48   5.712%   $30.1068   $30.11   $30.10   $30.10  
  Purchase #6 $139.61   8.238%   $151.1111   $151.11   $151.10   $151.10  
  Purchase #7 $148.91   4.639%   $155.8179   $155.82   $155.80   $155.80  
  7 purchase totals = $704.15       $763.4428   $763.45   $763.40   $763.40