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 $43.75   13.166%   $49.5101   $49.51   $49.50   $49.50  
  Purchase #2 $88.48   4.755%   $92.6872   $92.69   $92.70   $92.70  
  Purchase #3 $60.70   10.577%   $67.1202   $67.12   $67.10   $67.10  
  Purchase #4 $222.34   4.465%   $232.2675   $232.27   $232.25   $232.30  
  Purchase #5 $203.93   3.418%   $210.9003   $210.90   $210.90   $210.90  
  Purchase #6 $30.80   8.156%   $33.312   $33.31   $33.30   $33.30  
  Purchase #7 $218.34   5.259%   $229.8225   $229.82   $229.80   $229.80  
  7 purchase totals = $868.34       $915.6198   $915.62   $915.55   $915.60