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 $50.30   11.227%   $55.9472   $55.95   $55.95   $55.90  
  Purchase #2 $211.30   11.113%   $234.7818   $234.78   $234.80   $234.80  
  Purchase #3 $215.46   8.321%   $233.3884   $233.39   $233.40   $233.40  
  Purchase #4 $27.37   11.223%   $30.4417   $30.44   $30.45   $30.40  
  Purchase #5 $206.81   9.627%   $226.7196   $226.72   $226.70   $226.70  
  Purchase #6 $237.64   13.286%   $269.2129   $269.21   $269.20   $269.20  
  Purchase #7 $187.81   3.742%   $194.8379   $194.84   $194.85   $194.80  
  7 purchase totals = $1,136.69       $1,245.3295   $1,245.33   $1,245.35   $1,245.20