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 $167.85   11.575%   $187.2786   $187.28   $187.30   $187.30  
  Purchase #2 $56.84   9.435%   $62.2029   $62.20   $62.20   $62.20  
  Purchase #3 $59.61   8.481%   $64.6655   $64.67   $64.65   $64.70  
  Purchase #4 $151.42   11.171%   $168.3351   $168.34   $168.35   $168.30  
  Purchase #5 $102.89   10.722%   $113.9219   $113.92   $113.90   $113.90  
  Purchase #6 $114.43   6.832%   $122.2479   $122.25   $122.25   $122.20  
  Purchase #7 $12.47   6.311%   $13.257   $13.26   $13.25   $13.30  
  7 purchase totals = $665.51       $731.9089   $731.92   $731.90   $731.90