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 $149.45   11.109%   $166.0524   $166.05   $166.05   $166.10  
  Purchase #2 $242.37   4.592%   $253.4996   $253.50   $253.50   $253.50  
  Purchase #3 $106.61   3.389%   $110.223   $110.22   $110.20   $110.20  
  Purchase #4 $25.33   8.174%   $27.4005   $27.40   $27.40   $27.40  
  Purchase #5 $85.99   13.835%   $97.8867   $97.89   $97.90   $97.90  
  Purchase #6 $241.39   11.158%   $268.3243   $268.32   $268.30   $268.30  
  Purchase #7 $26.48   10.778%   $29.334   $29.33   $29.35   $29.30  
  7 purchase totals = $877.62       $952.7205   $952.71   $952.70   $952.70