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 $240.25   12.181%   $269.5149   $269.51   $269.50   $269.50  
  Purchase #2 $58.88   13.616%   $66.8971   $66.90   $66.90   $66.90  
  Purchase #3 $62.41   10.731%   $69.1072   $69.11   $69.10   $69.10  
  Purchase #4 $209.49   7.635%   $225.4846   $225.48   $225.50   $225.50  
  Purchase #5 $204.95   11.234%   $227.9741   $227.97   $227.95   $228.00  
  Purchase #6 $15.26   7.767%   $16.4452   $16.45   $16.45   $16.40  
  Purchase #7 $142.57   8.734%   $155.0221   $155.02   $155.00   $155.00  
  7 purchase totals = $933.81       $1,030.4452   $1,030.44   $1,030.40   $1,030.40