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 $66.84   6.473%   $71.1666   $71.17   $71.15   $71.20  
  Purchase #2 $62.66   9.603%   $68.6772   $68.68   $68.70   $68.70  
  Purchase #3 $187.28   6.646%   $199.7266   $199.73   $199.75   $199.70  
  Purchase #4 $216.34   5.271%   $227.7433   $227.74   $227.75   $227.70  
  Purchase #5 $70.77   13.719%   $80.4789   $80.48   $80.50   $80.50  
  Purchase #6 $119.28   9.415%   $130.5102   $130.51   $130.50   $130.50  
  Purchase #7 $219.65   7.755%   $236.6839   $236.68   $236.70   $236.70  
  7 purchase totals = $942.82       $1,014.9867   $1,014.99   $1,015.05   $1,015.00