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 $183.75   5.411%   $193.6927   $193.69   $193.70   $193.70  
  Purchase #2 $227.96   11.855%   $254.9847   $254.98   $255.00   $255.00  
  Purchase #3 $18.60   10.357%   $20.5264   $20.53   $20.55   $20.50  
  Purchase #4 $218.95   6.737%   $233.7007   $233.70   $233.70   $233.70  
  Purchase #5 $71.99   6.760%   $76.8565   $76.86   $76.85   $76.90  
  Purchase #6 $69.60   9.402%   $76.1438   $76.14   $76.15   $76.10  
  Purchase #7 $74.50   10.411%   $82.2562   $82.26   $82.25   $82.30  
  7 purchase totals = $865.35       $938.1610   $938.16   $938.20   $938.20