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 $32.62   6.268%   $34.6646   $34.66   $34.65   $34.70  
  Purchase #2 $109.86   3.285%   $113.4689   $113.47   $113.45   $113.50  
  Purchase #3 $60.95   4.161%   $63.4861   $63.49   $63.50   $63.50  
  Purchase #4 $59.51   9.483%   $65.1533   $65.15   $65.15   $65.20  
  Purchase #5 $160.49   12.692%   $180.8594   $180.86   $180.85   $180.90  
  Purchase #6 $14.78   13.493%   $16.7743   $16.77   $16.75   $16.80  
  Purchase #7 $127.35   11.496%   $141.9902   $141.99   $142.00   $142.00  
  7 purchase totals = $565.56       $616.3968   $616.39   $616.35   $616.60