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 $69.83   5.187%   $73.4521   $73.45   $73.45   $73.50  
  Purchase #2 $101.61   4.211%   $105.8888   $105.89   $105.90   $105.90  
  Purchase #3 $230.28   4.135%   $239.8021   $239.80   $239.80   $239.80  
  Purchase #4 $51.31   13.843%   $58.4128   $58.41   $58.40   $58.40  
  Purchase #5 $46.75   13.822%   $53.2118   $53.21   $53.20   $53.20  
  Purchase #6 $221.88   11.565%   $247.5404   $247.54   $247.55   $247.50  
  Purchase #7 $153.72   5.840%   $162.6972   $162.70   $162.70   $162.70  
  7 purchase totals = $875.38       $941.0052   $941.00   $941.00   $941.00