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 $201.45   8.585%   $218.7445   $218.74   $218.75   $218.70  
  Purchase #2 $229.26   3.662%   $237.6555   $237.66   $237.65   $237.70  
  Purchase #3 $236.78   10.605%   $261.8905   $261.89   $261.90   $261.90  
  Purchase #4 $180.72   10.621%   $199.9143   $199.91   $199.90   $199.90  
  Purchase #5 $189.57   5.771%   $200.5101   $200.51   $200.50   $200.50  
  Purchase #6 $68.34   11.184%   $75.9831   $75.98   $76.00   $76.00  
  Purchase #7 $110.92   4.186%   $115.5631   $115.56   $115.55   $115.60  
  7 purchase totals = $1,217.04       $1,310.2611   $1,310.25   $1,310.25   $1,310.30