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 $68.73   13.681%   $78.133   $78.13   $78.15   $78.10  
  Purchase #2 $154.37   12.617%   $173.8469   $173.85   $173.85   $173.80  
  Purchase #3 $162.55   11.119%   $180.6239   $180.62   $180.60   $180.60  
  Purchase #4 $70.67   3.242%   $72.9611   $72.96   $72.95   $73.00  
  Purchase #5 $227.60   12.307%   $255.6107   $255.61   $255.60   $255.60  
  Purchase #6 $87.25   11.175%   $97.0002   $97.00   $97.00   $97.00  
  Purchase #7 $226.95   5.617%   $239.6978   $239.70   $239.70   $239.70  
  7 purchase totals = $998.12       $1,097.8736   $1,097.87   $1,097.85   $1,097.80