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 $119.46   11.234%   $132.8801   $132.88   $132.90   $132.90  
  Purchase #2 $228.37   10.132%   $251.5084   $251.51   $251.50   $251.50  
  Purchase #3 $44.33   11.327%   $49.3513   $49.35   $49.35   $49.40  
  Purchase #4 $218.87   7.220%   $234.6724   $234.67   $234.65   $234.70  
  Purchase #5 $135.88   3.145%   $140.1534   $140.15   $140.15   $140.20  
  Purchase #6 $184.94   12.843%   $208.6918   $208.69   $208.70   $208.70  
  Purchase #7 $30.34   12.305%   $34.0733   $34.07   $34.05   $34.10  
  7 purchase totals = $962.19       $1,051.3307   $1,051.32   $1,051.30   $1,051.50