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 $56.43   9.762%   $61.9387   $61.94   $61.95   $61.90  
  Purchase #2 $56.52   3.812%   $58.6745   $58.67   $58.65   $58.70  
  Purchase #3 $247.55   10.697%   $274.0304   $274.03   $274.05   $274.00  
  Purchase #4 $243.52   7.224%   $261.1119   $261.11   $261.10   $261.10  
  Purchase #5 $223.95   5.438%   $236.1284   $236.13   $236.15   $236.10  
  Purchase #6 $154.46   5.839%   $163.4789   $163.48   $163.50   $163.50  
  Purchase #7 $234.94   6.672%   $250.6152   $250.62   $250.60   $250.60  
  7 purchase totals = $1,217.37       $1,305.9780   $1,305.98   $1,306.00   $1,305.90