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 $207.27   13.766%   $235.8028   $235.80   $235.80   $235.80  
  Purchase #2 $124.74   11.362%   $138.913   $138.91   $138.90   $138.90  
  Purchase #3 $248.43   5.248%   $261.4676   $261.47   $261.45   $261.50  
  Purchase #4 $152.53   11.594%   $170.2143   $170.21   $170.20   $170.20  
  Purchase #5 $89.83   8.387%   $97.364   $97.36   $97.35   $97.40  
  Purchase #6 $246.64   9.210%   $269.3555   $269.36   $269.35   $269.40  
  Purchase #7 $147.84   4.474%   $154.4544   $154.45   $154.45   $154.50  
  7 purchase totals = $1,217.28       $1,327.5716   $1,327.56   $1,327.50   $1,327.70