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 $121.97   3.301%   $125.9962   $126.00   $126.00   $126.00  
  Purchase #2 $176.28   10.623%   $195.0062   $195.01   $195.00   $195.00  
  Purchase #3 $66.32   10.149%   $73.0508   $73.05   $73.05   $73.10  
  Purchase #4 $77.57   13.518%   $88.0559   $88.06   $88.05   $88.10  
  Purchase #5 $190.73   4.207%   $198.754   $198.75   $198.75   $198.80  
  Purchase #6 $172.77   11.684%   $192.9564   $192.96   $192.95   $193.00  
  Purchase #7 $207.54   12.717%   $233.9329   $233.93   $233.95   $233.90  
  7 purchase totals = $1,013.18       $1,107.7524   $1,107.76   $1,107.75   $1,107.90