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 $232.83   12.501%   $261.9361   $261.94   $261.95   $261.90  
  Purchase #2 $110.40   10.679%   $122.1896   $122.19   $122.20   $122.20  
  Purchase #3 $94.88   7.774%   $102.256   $102.26   $102.25   $102.30  
  Purchase #4 $169.51   5.170%   $178.2737   $178.27   $178.25   $178.30  
  Purchase #5 $41.67   6.460%   $44.3619   $44.36   $44.35   $44.40  
  Purchase #6 $101.71   11.791%   $113.7026   $113.70   $113.70   $113.70  
  Purchase #7 $214.39   12.272%   $240.6999   $240.70   $240.70   $240.70  
  7 purchase totals = $965.39       $1,063.4198   $1,063.42   $1,063.40   $1,063.50