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 $211.53   11.573%   $236.0104   $236.01   $236.00   $236.00  
  Purchase #2 $79.97   4.590%   $83.6406   $83.64   $83.65   $83.60  
  Purchase #3 $30.58   8.384%   $33.1438   $33.14   $33.15   $33.10  
  Purchase #4 $181.93   9.627%   $199.4444   $199.44   $199.45   $199.40  
  Purchase #5 $56.31   10.205%   $62.0564   $62.06   $62.05   $62.10  
  Purchase #6 $95.50   8.476%   $103.5946   $103.59   $103.60   $103.60  
  Purchase #7 $19.87   13.119%   $22.4767   $22.48   $22.50   $22.50  
  7 purchase totals = $675.69       $740.3669   $740.36   $740.40   $740.30