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 $119.48   4.369%   $124.7001   $124.70   $124.70   $124.70  
  Purchase #2 $88.97   5.648%   $93.995   $94.00   $94.00   $94.00  
  Purchase #3 $10.90   8.470%   $11.8232   $11.82   $11.80   $11.80  
  Purchase #4 $26.55   12.617%   $29.8998   $29.90   $29.90   $29.90  
  Purchase #5 $197.44   9.501%   $216.1988   $216.20   $216.20   $216.20  
  Purchase #6 $208.50   11.867%   $233.2427   $233.24   $233.25   $233.20  
  Purchase #7 $114.78   10.211%   $126.5002   $126.50   $126.50   $126.50  
  7 purchase totals = $766.62       $836.3598   $836.36   $836.35   $836.30