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 $227.41   9.837%   $249.7803   $249.78   $249.80   $249.80  
  Purchase #2 $177.61   8.205%   $192.1829   $192.18   $192.20   $192.20  
  Purchase #3 $44.72   12.158%   $50.1571   $50.16   $50.15   $50.20  
  Purchase #4 $24.40   8.865%   $26.5631   $26.56   $26.55   $26.60  
  Purchase #5 $216.62   6.871%   $231.504   $231.50   $231.50   $231.50  
  Purchase #6 $171.88   13.177%   $194.5286   $194.53   $194.55   $194.50  
  Purchase #7 $92.71   7.350%   $99.5242   $99.52   $99.50   $99.50  
  7 purchase totals = $955.35       $1,044.2402   $1,044.23   $1,044.25   $1,044.30