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 $38.93   5.396%   $41.0307   $41.03   $41.05   $41.00  
  Purchase #2 $163.58   10.664%   $181.0242   $181.02   $181.00   $181.00  
  Purchase #3 $171.36   9.103%   $186.9589   $186.96   $186.95   $187.00  
  Purchase #4 $236.72   6.468%   $252.031   $252.03   $252.05   $252.00  
  Purchase #5 $79.96   10.173%   $88.0943   $88.09   $88.10   $88.10  
  Purchase #6 $182.99   8.105%   $197.8213   $197.82   $197.80   $197.80  
  Purchase #7 $214.76   13.572%   $243.9072   $243.91   $243.90   $243.90  
  7 purchase totals = $1,088.30       $1,190.8676   $1,190.86   $1,190.85   $1,190.80