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 $119.56   3.527%   $123.7769   $123.78   $123.80   $123.80  
  Purchase #2 $5.37   4.856%   $5.6308   $5.63   $5.65   $5.60  
  Purchase #3 $104.55   13.829%   $119.0082   $119.01   $119.00   $119.00  
  Purchase #4 $234.26   6.623%   $249.775   $249.78   $249.80   $249.80  
  Purchase #5 $113.60   9.695%   $124.6135   $124.61   $124.60   $124.60  
  Purchase #6 $6.77   5.502%   $7.1425   $7.14   $7.15   $7.10  
  Purchase #7 $82.60   6.847%   $88.2556   $88.26   $88.25   $88.30  
  7 purchase totals = $666.71       $718.2025   $718.21   $718.25   $718.20