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 $243.37   7.674%   $262.0462   $262.05   $262.05   $262.00  
  Purchase #2 $105.61   13.514%   $119.8821   $119.88   $119.90   $119.90  
  Purchase #3 $193.85   3.718%   $201.0573   $201.06   $201.05   $201.10  
  Purchase #4 $9.94   12.651%   $11.1975   $11.20   $11.20   $11.20  
  Purchase #5 $132.48   6.129%   $140.5997   $140.60   $140.60   $140.60  
  Purchase #6 $48.39   13.510%   $54.9275   $54.93   $54.95   $54.90  
  Purchase #7 $87.68   8.671%   $95.2827   $95.28   $95.30   $95.30  
  7 purchase totals = $821.32       $884.9930   $885.00   $885.05   $885.00