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 $132.61   11.143%   $147.3867   $147.39   $147.40   $147.40  
  Purchase #2 $101.97   6.663%   $108.7643   $108.76   $108.75   $108.80  
  Purchase #3 $56.48   13.187%   $63.928   $63.93   $63.95   $63.90  
  Purchase #4 $240.32   5.612%   $253.8068   $253.81   $253.80   $253.80  
  Purchase #5 $136.41   9.417%   $149.2557   $149.26   $149.25   $149.30  
  Purchase #6 $161.75   7.163%   $173.3362   $173.34   $173.35   $173.30  
  Purchase #7 $50.35   6.352%   $53.5482   $53.55   $53.55   $53.50  
  7 purchase totals = $879.89       $950.0259   $950.04   $950.05   $950.00