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 $240.60   11.783%   $268.9499   $268.95   $268.95   $268.90  
  Purchase #2 $24.30   7.181%   $26.045   $26.05   $26.05   $26.00  
  Purchase #3 $214.91   4.103%   $223.7278   $223.73   $223.75   $223.70  
  Purchase #4 $97.87   12.766%   $110.3641   $110.36   $110.35   $110.40  
  Purchase #5 $96.29   7.603%   $103.6109   $103.61   $103.60   $103.60  
  Purchase #6 $200.33   10.747%   $221.8595   $221.86   $221.85   $221.90  
  Purchase #7 $57.81   5.733%   $61.1242   $61.12   $61.10   $61.10  
  7 purchase totals = $932.11       $1,015.6814   $1,015.68   $1,015.65   $1,015.60