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 $28.99   13.662%   $32.9506   $32.95   $32.95   $33.00  
  Purchase #2 $34.93   3.596%   $36.1861   $36.19   $36.20   $36.20  
  Purchase #3 $70.99   10.631%   $78.5369   $78.54   $78.55   $78.50  
  Purchase #4 $157.30   11.830%   $175.9086   $175.91   $175.90   $175.90  
  Purchase #5 $194.52   7.309%   $208.7375   $208.74   $208.75   $208.70  
  Purchase #6 $191.93   4.268%   $200.1216   $200.12   $200.10   $200.10  
  Purchase #7 $22.88   7.552%   $24.6079   $24.61   $24.60   $24.60  
  7 purchase totals = $701.54       $757.0492   $757.06   $757.05   $757.00