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 $33.34   9.743%   $36.5883   $36.59   $36.60   $36.60  
  Purchase #2 $187.32   5.147%   $196.9614   $196.96   $196.95   $197.00  
  Purchase #3 $112.74   13.216%   $127.6397   $127.64   $127.65   $127.60  
  Purchase #4 $242.27   8.199%   $262.1337   $262.13   $262.15   $262.10  
  Purchase #5 $104.38   12.188%   $117.1018   $117.10   $117.10   $117.10  
  Purchase #6 $88.70   4.869%   $93.0188   $93.02   $93.00   $93.00  
  Purchase #7 $34.31   4.264%   $35.773   $35.77   $35.75   $35.80  
  7 purchase totals = $803.06       $869.2167   $869.21   $869.20   $869.20