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 $65.65   5.455%   $69.2312   $69.23   $69.25   $69.20  
  Purchase #2 $225.44   10.859%   $249.9205   $249.92   $249.90   $249.90  
  Purchase #3 $132.58   12.107%   $148.6315   $148.63   $148.65   $148.60  
  Purchase #4 $185.74   8.612%   $201.7359   $201.74   $201.75   $201.70  
  Purchase #5 $162.43   12.849%   $183.3006   $183.30   $183.30   $183.30  
  Purchase #6 $110.63   9.726%   $121.3899   $121.39   $121.40   $121.40  
  Purchase #7 $232.89   4.767%   $243.9919   $243.99   $244.00   $244.00  
  7 purchase totals = $1,115.36       $1,218.2015   $1,218.20   $1,218.25   $1,218.10