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 $154.98   6.211%   $164.6058   $164.61   $164.60   $164.60  
  Purchase #2 $188.25   11.383%   $209.6785   $209.68   $209.70   $209.70  
  Purchase #3 $123.29   10.449%   $136.1726   $136.17   $136.15   $136.20  
  Purchase #4 $169.61   6.554%   $180.7262   $180.73   $180.75   $180.70  
  Purchase #5 $82.49   12.780%   $93.0322   $93.03   $93.05   $93.00  
  Purchase #6 $208.42   3.271%   $215.2374   $215.24   $215.25   $215.20  
  Purchase #7 $170.69   6.465%   $181.7251   $181.73   $181.75   $181.70  
  7 purchase totals = $1,097.73       $1,181.1778   $1,181.19   $1,181.25   $1,181.10