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 $144.78   4.629%   $151.4819   $151.48   $151.50   $151.50  
  Purchase #2 $198.43   13.730%   $225.6744   $225.67   $225.65   $225.70  
  Purchase #3 $58.73   13.381%   $66.5887   $66.59   $66.60   $66.60  
  Purchase #4 $244.66   6.827%   $261.3629   $261.36   $261.35   $261.40  
  Purchase #5 $244.45   9.339%   $267.2792   $267.28   $267.30   $267.30  
  Purchase #6 $163.93   6.385%   $174.3969   $174.40   $174.40   $174.40  
  Purchase #7 $82.75   13.622%   $94.0222   $94.02   $94.00   $94.00  
  7 purchase totals = $1,137.73       $1,240.8062   $1,240.80   $1,240.80   $1,240.90