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 $60.61   6.275%   $64.4133   $64.41   $64.40   $64.40  
  Purchase #2 $124.26   13.769%   $141.3694   $141.37   $141.35   $141.40  
  Purchase #3 $215.88   3.470%   $223.371   $223.37   $223.35   $223.40  
  Purchase #4 $191.75   5.510%   $202.3154   $202.32   $202.30   $202.30  
  Purchase #5 $23.86   12.374%   $26.8124   $26.81   $26.80   $26.80  
  Purchase #6 $193.95   12.473%   $218.1414   $218.14   $218.15   $218.10  
  Purchase #7 $245.40   11.657%   $274.0063   $274.01   $274.00   $274.00  
  7 purchase totals = $1,055.71       $1,150.4292   $1,150.43   $1,150.35   $1,150.40