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 $240.61   11.497%   $268.2729   $268.27   $268.25   $268.30  
  Purchase #2 $58.46   13.667%   $66.4497   $66.45   $66.45   $66.40  
  Purchase #3 $16.87   7.173%   $18.0801   $18.08   $18.10   $18.10  
  Purchase #4 $242.66   7.766%   $261.505   $261.51   $261.50   $261.50  
  Purchase #5 $10.97   10.436%   $12.1148   $12.11   $12.10   $12.10  
  Purchase #6 $166.63   7.469%   $179.0756   $179.08   $179.10   $179.10  
  Purchase #7 $230.57   10.375%   $254.4916   $254.49   $254.50   $254.50  
  7 purchase totals = $966.77       $1,059.9897   $1,059.99   $1,060.00   $1,060.00