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 $151.94   8.573%   $164.9658   $164.97   $164.95   $165.00  
  Purchase #2 $213.37   10.429%   $235.6224   $235.62   $235.60   $235.60  
  Purchase #3 $247.31   9.252%   $270.1911   $270.19   $270.20   $270.20  
  Purchase #4 $231.28   4.186%   $240.9614   $240.96   $240.95   $241.00  
  Purchase #5 $57.48   5.362%   $60.5621   $60.56   $60.55   $60.60  
  Purchase #6 $165.45   8.324%   $179.2221   $179.22   $179.20   $179.20  
  Purchase #7 $112.73   3.448%   $116.6169   $116.62   $116.60   $116.60  
  7 purchase totals = $1,179.56       $1,268.1418   $1,268.14   $1,268.05   $1,268.20