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 $58.46   11.723%   $65.3133   $65.31   $65.30   $65.30  
  Purchase #2 $180.59   8.695%   $196.2923   $196.29   $196.30   $196.30  
  Purchase #3 $249.31   5.840%   $263.8697   $263.87   $263.85   $263.90  
  Purchase #4 $233.63   9.691%   $256.2711   $256.27   $256.25   $256.30  
  Purchase #5 $166.61   4.288%   $173.7542   $173.75   $173.75   $173.80  
  Purchase #6 $24.80   6.253%   $26.3507   $26.35   $26.35   $26.40  
  Purchase #7 $245.61   4.800%   $257.3993   $257.40   $257.40   $257.40  
  7 purchase totals = $1,159.01       $1,239.2506   $1,239.24   $1,239.20   $1,239.40