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 $69.66   12.189%   $78.1509   $78.15   $78.15   $78.20  
  Purchase #2 $77.75   7.214%   $83.3589   $83.36   $83.35   $83.40  
  Purchase #3 $66.58   3.598%   $68.9755   $68.98   $69.00   $69.00  
  Purchase #4 $68.55   6.774%   $73.1936   $73.19   $73.20   $73.20  
  Purchase #5 $96.31   5.123%   $101.244   $101.24   $101.25   $101.20  
  Purchase #6 $78.62   7.670%   $84.6502   $84.65   $84.65   $84.70  
  Purchase #7 $67.54   10.524%   $74.6479   $74.65   $74.65   $74.60  
  7 purchase totals = $525.01       $564.2210   $564.22   $564.25   $564.30