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 $175.73   10.127%   $193.5262   $193.53   $193.55   $193.50  
  Purchase #2 $139.95   9.298%   $152.9626   $152.96   $152.95   $153.00  
  Purchase #3 $190.36   4.397%   $198.7301   $198.73   $198.75   $198.70  
  Purchase #4 $226.77   9.251%   $247.7485   $247.75   $247.75   $247.70  
  Purchase #5 $25.80   13.458%   $29.2722   $29.27   $29.25   $29.30  
  Purchase #6 $51.33   8.212%   $55.5452   $55.55   $55.55   $55.50  
  Purchase #7 $217.81   13.439%   $247.0815   $247.08   $247.10   $247.10  
  7 purchase totals = $1,027.75       $1,124.8663   $1,124.87   $1,124.90   $1,124.80