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 $20.65   6.615%   $22.016   $22.02   $22.00   $22.00  
  Purchase #2 $249.77   13.826%   $284.3032   $284.30   $284.30   $284.30  
  Purchase #3 $77.32   12.542%   $87.0175   $87.02   $87.00   $87.00  
  Purchase #4 $218.73   10.126%   $240.8786   $240.88   $240.90   $240.90  
  Purchase #5 $114.51   12.667%   $129.015   $129.02   $129.00   $129.00  
  Purchase #6 $68.40   10.488%   $75.5738   $75.57   $75.55   $75.60  
  Purchase #7 $236.39   4.477%   $246.9732   $246.97   $246.95   $247.00  
  7 purchase totals = $985.77       $1,085.7773   $1,085.78   $1,085.70   $1,085.80