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 $216.94   7.729%   $233.7073   $233.71   $233.70   $233.70  
  Purchase #2 $222.52   4.187%   $231.8369   $231.84   $231.85   $231.80  
  Purchase #3 $188.28   12.388%   $211.6041   $211.60   $211.60   $211.60  
  Purchase #4 $63.71   4.573%   $66.6235   $66.62   $66.60   $66.60  
  Purchase #5 $160.83   9.607%   $176.2809   $176.28   $176.30   $176.30  
  Purchase #6 $146.55   8.174%   $158.529   $158.53   $158.55   $158.50  
  Purchase #7 $246.26   6.382%   $261.9763   $261.98   $262.00   $262.00  
  7 purchase totals = $1,245.09       $1,340.5580   $1,340.56   $1,340.60   $1,340.50