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 $210.67   12.629%   $237.2755   $237.28   $237.30   $237.30  
  Purchase #2 $249.55   5.256%   $262.6663   $262.67   $262.65   $262.70  
  Purchase #3 $86.41   7.228%   $92.6557   $92.66   $92.65   $92.70  
  Purchase #4 $203.61   12.129%   $228.3059   $228.31   $228.30   $228.30  
  Purchase #5 $69.86   13.662%   $79.4043   $79.40   $79.40   $79.40  
  Purchase #6 $66.89   8.805%   $72.7797   $72.78   $72.80   $72.80  
  Purchase #7 $225.58   13.585%   $256.225   $256.23   $256.25   $256.20  
  7 purchase totals = $1,112.57       $1,229.3124   $1,229.33   $1,229.35   $1,229.40