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 $202.62   6.597%   $215.9868   $215.99   $216.00   $216.00  
  Purchase #2 $15.79   3.321%   $16.3144   $16.31   $16.30   $16.30  
  Purchase #3 $63.63   7.293%   $68.2705   $68.27   $68.25   $68.30  
  Purchase #4 $110.93   12.429%   $124.7175   $124.72   $124.70   $124.70  
  Purchase #5 $180.26   3.709%   $186.9458   $186.95   $186.95   $186.90  
  Purchase #6 $51.31   6.871%   $54.8355   $54.84   $54.85   $54.80  
  Purchase #7 $150.41   6.124%   $159.6211   $159.62   $159.60   $159.60  
  7 purchase totals = $774.95       $826.6916   $826.70   $826.65   $826.60