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 $25.32   4.794%   $26.5338   $26.53   $26.55   $26.50  
  Purchase #2 $88.76   7.794%   $95.678   $95.68   $95.70   $95.70  
  Purchase #3 $138.75   11.521%   $154.7354   $154.74   $154.75   $154.70  
  Purchase #4 $210.45   7.567%   $226.3748   $226.37   $226.35   $226.40  
  Purchase #5 $245.72   5.211%   $258.5245   $258.52   $258.50   $258.50  
  Purchase #6 $146.42   3.566%   $151.6413   $151.64   $151.65   $151.60  
  Purchase #7 $138.67   10.606%   $153.3773   $153.38   $153.40   $153.40  
  7 purchase totals = $994.09       $1,066.8651   $1,066.86   $1,066.90   $1,066.80