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 $86.96   8.424%   $94.2855   $94.29   $94.30   $94.30  
  Purchase #2 $100.58   12.279%   $112.9302   $112.93   $112.95   $112.90  
  Purchase #3 $115.29   12.868%   $130.1255   $130.13   $130.15   $130.10  
  Purchase #4 $153.45   5.714%   $162.2181   $162.22   $162.20   $162.20  
  Purchase #5 $102.60   12.414%   $115.3368   $115.34   $115.35   $115.30  
  Purchase #6 $154.30   13.330%   $174.8682   $174.87   $174.85   $174.90  
  Purchase #7 $73.36   11.418%   $81.7362   $81.74   $81.75   $81.70  
  7 purchase totals = $786.54       $871.5005   $871.52   $871.55   $871.40