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 $171.36   12.839%   $193.3609   $193.36   $193.35   $193.40  
  Purchase #2 $205.93   13.756%   $234.2577   $234.26   $234.25   $234.30  
  Purchase #3 $222.97   9.699%   $244.5959   $244.60   $244.60   $244.60  
  Purchase #4 $53.75   6.722%   $57.3631   $57.36   $57.35   $57.40  
  Purchase #5 $237.36   6.789%   $253.4744   $253.47   $253.45   $253.50  
  Purchase #6 $151.96   6.214%   $161.4028   $161.40   $161.40   $161.40  
  Purchase #7 $85.62   13.632%   $97.2917   $97.29   $97.30   $97.30  
  7 purchase totals = $1,128.95       $1,241.7465   $1,241.74   $1,241.70   $1,241.90