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 $134.85   3.766%   $139.9285   $139.93   $139.95   $139.90  
  Purchase #2 $69.38   7.348%   $74.478   $74.48   $74.50   $74.50  
  Purchase #3 $97.43   6.217%   $103.4872   $103.49   $103.50   $103.50  
  Purchase #4 $23.99   13.534%   $27.2368   $27.24   $27.25   $27.20  
  Purchase #5 $205.82   4.227%   $214.52   $214.52   $214.50   $214.50  
  Purchase #6 $53.98   3.719%   $55.9875   $55.99   $56.00   $56.00  
  Purchase #7 $151.67   13.294%   $171.833   $171.83   $171.85   $171.80  
  7 purchase totals = $737.12       $787.4710   $787.48   $787.55   $787.40