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 $233.73   12.739%   $263.5049   $263.50   $263.50   $263.50  
  Purchase #2 $7.73   13.767%   $8.7942   $8.79   $8.80   $8.80  
  Purchase #3 $211.68   9.316%   $231.4001   $231.40   $231.40   $231.40  
  Purchase #4 $109.58   9.452%   $119.9375   $119.94   $119.95   $119.90  
  Purchase #5 $63.70   4.360%   $66.4773   $66.48   $66.50   $66.50  
  Purchase #6 $129.27   9.734%   $141.8531   $141.85   $141.85   $141.90  
  Purchase #7 $207.79   8.771%   $226.0153   $226.02   $226.00   $226.00  
  7 purchase totals = $963.48       $1,057.9824   $1,057.98   $1,058.00   $1,058.00