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 $105.47   7.391%   $113.2653   $113.27   $113.25   $113.30  
  Purchase #2 $88.62   6.468%   $94.3519   $94.35   $94.35   $94.40  
  Purchase #3 $87.44   5.432%   $92.1897   $92.19   $92.20   $92.20  
  Purchase #4 $232.28   13.255%   $263.0687   $263.07   $263.05   $263.10  
  Purchase #5 $49.76   3.715%   $51.6086   $51.61   $51.60   $51.60  
  Purchase #6 $209.75   11.764%   $234.425   $234.43   $234.45   $234.40  
  Purchase #7 $203.87   6.176%   $216.461   $216.46   $216.45   $216.50  
  7 purchase totals = $977.19       $1,065.3702   $1,065.38   $1,065.35   $1,065.50