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 $182.49   7.712%   $196.5636   $196.56   $196.55   $196.60  
  Purchase #2 $175.40   12.497%   $197.3197   $197.32   $197.30   $197.30  
  Purchase #3 $6.25   7.130%   $6.6956   $6.70   $6.70   $6.70  
  Purchase #4 $15.95   12.348%   $17.9195   $17.92   $17.90   $17.90  
  Purchase #5 $139.72   6.761%   $149.1665   $149.17   $149.15   $149.20  
  Purchase #6 $202.40   8.827%   $220.2658   $220.27   $220.25   $220.30  
  Purchase #7 $184.29   12.621%   $207.5492   $207.55   $207.55   $207.50  
  7 purchase totals = $906.50       $995.4799   $995.49   $995.40   $995.50