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 $62.47   6.618%   $66.6043   $66.60   $66.60   $66.60  
  Purchase #2 $96.70   13.722%   $109.9692   $109.97   $109.95   $110.00  
  Purchase #3 $30.30   12.193%   $33.9945   $33.99   $34.00   $34.00  
  Purchase #4 $213.53   13.738%   $242.8648   $242.86   $242.85   $242.90  
  Purchase #5 $192.99   9.364%   $211.0616   $211.06   $211.05   $211.10  
  Purchase #6 $163.76   6.633%   $174.6222   $174.62   $174.60   $174.60  
  Purchase #7 $203.42   8.572%   $220.8572   $220.86   $220.85   $220.90  
  7 purchase totals = $963.17       $1,059.9738   $1,059.96   $1,059.90   $1,060.10