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 $249.67   7.150%   $267.5214   $267.52   $267.50   $267.50  
  Purchase #2 $104.90   6.470%   $111.687   $111.69   $111.70   $111.70  
  Purchase #3 $68.86   11.701%   $76.9173   $76.92   $76.90   $76.90  
  Purchase #4 $139.43   6.465%   $148.4441   $148.44   $148.45   $148.40  
  Purchase #5 $6.48   11.500%   $7.2252   $7.23   $7.25   $7.20  
  Purchase #6 $81.86   3.111%   $84.4067   $84.41   $84.40   $84.40  
  Purchase #7 $44.41   10.439%   $49.046   $49.05   $49.05   $49.00  
  7 purchase totals = $695.61       $745.2477   $745.26   $745.25   $745.10