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 $249.86   7.131%   $267.6775   $267.68   $267.70   $267.70  
  Purchase #2 $34.76   6.157%   $36.9002   $36.90   $36.90   $36.90  
  Purchase #3 $193.30   6.344%   $205.563   $205.56   $205.55   $205.60  
  Purchase #4 $218.63   5.706%   $231.105   $231.11   $231.10   $231.10  
  Purchase #5 $86.52   12.756%   $97.5565   $97.56   $97.55   $97.60  
  Purchase #6 $141.86   3.293%   $146.5314   $146.53   $146.55   $146.50  
  Purchase #7 $37.43   9.376%   $40.9394   $40.94   $40.95   $40.90  
  7 purchase totals = $962.36       $1,026.2730   $1,026.28   $1,026.30   $1,026.30