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 $237.90   10.134%   $262.0088   $262.01   $262.00   $262.00  
  Purchase #2 $13.53   6.835%   $14.4548   $14.45   $14.45   $14.50  
  Purchase #3 $47.96   7.759%   $51.6812   $51.68   $51.70   $51.70  
  Purchase #4 $216.55   11.148%   $240.691   $240.69   $240.70   $240.70  
  Purchase #5 $115.45   8.543%   $125.3129   $125.31   $125.30   $125.30  
  Purchase #6 $41.96   3.393%   $43.3837   $43.38   $43.40   $43.40  
  Purchase #7 $6.77   6.629%   $7.2188   $7.22   $7.20   $7.20  
  7 purchase totals = $680.12       $744.7512   $744.74   $744.75   $744.80