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 $223.49   8.814%   $243.1884   $243.19   $243.20   $243.20  
  Purchase #2 $248.25   7.111%   $265.9031   $265.90   $265.90   $265.90  
  Purchase #3 $103.40   8.310%   $111.9925   $111.99   $112.00   $112.00  
  Purchase #4 $95.69   7.430%   $102.7998   $102.80   $102.80   $102.80  
  Purchase #5 $237.61   12.327%   $266.9002   $266.90   $266.90   $266.90  
  Purchase #6 $211.41   9.492%   $231.477   $231.48   $231.50   $231.50  
  Purchase #7 $46.31   9.530%   $50.7233   $50.72   $50.70   $50.70  
  7 purchase totals = $1,166.16       $1,272.9843   $1,272.98   $1,273.00   $1,273.00