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 $56.75   9.314%   $62.0357   $62.04   $62.05   $62.00  
  Purchase #2 $23.87   9.607%   $26.1632   $26.16   $26.15   $26.20  
  Purchase #3 $191.67   11.834%   $214.3522   $214.35   $214.35   $214.40  
  Purchase #4 $171.65   9.413%   $187.8074   $187.81   $187.80   $187.80  
  Purchase #5 $154.90   8.412%   $167.9302   $167.93   $167.95   $167.90  
  Purchase #6 $224.56   9.371%   $245.6035   $245.60   $245.60   $245.60  
  Purchase #7 $51.46   8.268%   $55.7147   $55.71   $55.70   $55.70  
  7 purchase totals = $874.86       $959.6069   $959.60   $959.60   $959.60