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 $212.76   6.794%   $227.2149   $227.21   $227.20   $227.20  
  Purchase #2 $53.32   5.552%   $56.2803   $56.28   $56.30   $56.30  
  Purchase #3 $36.38   9.783%   $39.9391   $39.94   $39.95   $39.90  
  Purchase #4 $156.89   4.330%   $163.6833   $163.68   $163.70   $163.70  
  Purchase #5 $56.90   13.214%   $64.4188   $64.42   $64.40   $64.40  
  Purchase #6 $173.30   10.628%   $191.7183   $191.72   $191.70   $191.70  
  Purchase #7 $213.41   8.256%   $231.0291   $231.03   $231.05   $231.00  
  7 purchase totals = $902.96       $974.2838   $974.28   $974.30   $974.20