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 $154.90   13.424%   $175.6938   $175.69   $175.70   $175.70  
  Purchase #2 $147.69   4.642%   $154.5458   $154.55   $154.55   $154.50  
  Purchase #3 $160.78   4.106%   $167.3816   $167.38   $167.40   $167.40  
  Purchase #4 $55.93   8.532%   $60.7019   $60.70   $60.70   $60.70  
  Purchase #5 $237.37   13.238%   $268.793   $268.79   $268.80   $268.80  
  Purchase #6 $174.27   11.169%   $193.7342   $193.73   $193.75   $193.70  
  Purchase #7 $11.76   13.521%   $13.3501   $13.35   $13.35   $13.40  
  7 purchase totals = $942.70       $1,034.2004   $1,034.19   $1,034.25   $1,034.20