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 $55.50   11.757%   $62.0251   $62.03   $62.05   $62.00  
  Purchase #2 $75.73   8.123%   $81.8815   $81.88   $81.90   $81.90  
  Purchase #3 $56.74   3.166%   $58.5364   $58.54   $58.55   $58.50  
  Purchase #4 $93.26   10.263%   $102.8313   $102.83   $102.85   $102.80  
  Purchase #5 $38.36   5.826%   $40.5949   $40.59   $40.60   $40.60  
  Purchase #6 $235.65   5.348%   $248.2526   $248.25   $248.25   $248.30  
  Purchase #7 $34.79   8.429%   $37.7224   $37.72   $37.70   $37.70  
  7 purchase totals = $590.03       $631.8442   $631.84   $631.90   $631.80