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 $29.74   13.139%   $33.6475   $33.65   $33.65   $33.60  
  Purchase #2 $195.81   10.690%   $216.7421   $216.74   $216.75   $216.70  
  Purchase #3 $166.61   3.376%   $172.2348   $172.23   $172.25   $172.20  
  Purchase #4 $36.50   12.787%   $41.1673   $41.17   $41.15   $41.20  
  Purchase #5 $211.65   3.563%   $219.1911   $219.19   $219.20   $219.20  
  Purchase #6 $36.73   3.411%   $37.9829   $37.98   $38.00   $38.00  
  Purchase #7 $34.83   6.190%   $36.986   $36.99   $37.00   $37.00  
  7 purchase totals = $711.87       $757.9517   $757.95   $758.00   $757.90