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 $236.96   7.420%   $254.5424   $254.54   $254.55   $254.50  
  Purchase #2 $234.32   3.767%   $243.1468   $243.15   $243.15   $243.10  
  Purchase #3 $134.47   7.267%   $144.2419   $144.24   $144.25   $144.20  
  Purchase #4 $234.73   13.494%   $266.4045   $266.40   $266.40   $266.40  
  Purchase #5 $129.68   5.767%   $137.1586   $137.16   $137.15   $137.20  
  Purchase #6 $203.51   10.152%   $224.1703   $224.17   $224.15   $224.20  
  Purchase #7 $168.71   13.797%   $191.9869   $191.99   $192.00   $192.00  
  7 purchase totals = $1,342.38       $1,461.6514   $1,461.65   $1,461.65   $1,461.60