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 $61.44   9.552%   $67.3087   $67.31   $67.30   $67.30  
  Purchase #2 $248.97   5.812%   $263.4401   $263.44   $263.45   $263.40  
  Purchase #3 $131.57   3.642%   $136.3618   $136.36   $136.35   $136.40  
  Purchase #4 $129.71   7.270%   $139.1399   $139.14   $139.15   $139.10  
  Purchase #5 $137.77   8.375%   $149.3082   $149.31   $149.30   $149.30  
  Purchase #6 $229.65   4.615%   $240.2483   $240.25   $240.25   $240.20  
  Purchase #7 $101.61   8.388%   $110.133   $110.13   $110.15   $110.10  
  7 purchase totals = $1,040.72       $1,105.9400   $1,105.94   $1,105.95   $1,105.80