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 $234.69   10.243%   $258.7293   $258.73   $258.75   $258.70  
  Purchase #2 $229.26   10.247%   $252.7523   $252.75   $252.75   $252.80  
  Purchase #3 $8.37   4.773%   $8.7695   $8.77   $8.75   $8.80  
  Purchase #4 $89.50   6.545%   $95.3578   $95.36   $95.35   $95.40  
  Purchase #5 $196.31   11.342%   $218.5755   $218.58   $218.60   $218.60  
  Purchase #6 $149.42   12.217%   $167.6746   $167.67   $167.65   $167.70  
  Purchase #7 $227.98   5.155%   $239.7324   $239.73   $239.75   $239.70  
  7 purchase totals = $1,135.53       $1,241.5914   $1,241.59   $1,241.60   $1,241.70