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 $217.64   9.130%   $237.5105   $237.51   $237.50   $237.50  
  Purchase #2 $101.27   6.319%   $107.6693   $107.67   $107.65   $107.70  
  Purchase #3 $91.94   10.312%   $101.4209   $101.42   $101.40   $101.40  
  Purchase #4 $231.79   10.124%   $255.2564   $255.26   $255.25   $255.30  
  Purchase #5 $134.82   12.836%   $152.1255   $152.13   $152.15   $152.10  
  Purchase #6 $61.66   5.820%   $65.2486   $65.25   $65.25   $65.20  
  Purchase #7 $220.53   5.246%   $232.099   $232.10   $232.10   $232.10  
  7 purchase totals = $1,059.65       $1,151.3302   $1,151.34   $1,151.30   $1,151.30