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 $246.91   10.444%   $272.6973   $272.70   $272.70   $272.70  
  Purchase #2 $24.55   7.274%   $26.3358   $26.34   $26.35   $26.30  
  Purchase #3 $116.87   7.585%   $125.7346   $125.73   $125.75   $125.70  
  Purchase #4 $46.73   12.584%   $52.6105   $52.61   $52.60   $52.60  
  Purchase #5 $68.67   4.705%   $71.9009   $71.90   $71.90   $71.90  
  Purchase #6 $245.78   10.554%   $271.7196   $271.72   $271.70   $271.70  
  Purchase #7 $57.98   9.517%   $63.498   $63.50   $63.50   $63.50  
  7 purchase totals = $807.49       $884.4967   $884.50   $884.50   $884.40