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 $156.28   8.583%   $169.6935   $169.69   $169.70   $169.70  
  Purchase #2 $13.62   3.366%   $14.0784   $14.08   $14.10   $14.10  
  Purchase #3 $162.76   6.718%   $173.6942   $173.69   $173.70   $173.70  
  Purchase #4 $174.66   13.128%   $197.5894   $197.59   $197.60   $197.60  
  Purchase #5 $57.42   7.144%   $61.5221   $61.52   $61.50   $61.50  
  Purchase #6 $54.99   13.466%   $62.395   $62.40   $62.40   $62.40  
  Purchase #7 $140.41   3.820%   $145.7737   $145.77   $145.75   $145.80  
  7 purchase totals = $760.14       $824.7463   $824.74   $824.75   $824.80