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 $46.59   13.575%   $52.9146   $52.91   $52.90   $52.90  
  Purchase #2 $71.99   5.708%   $76.0992   $76.10   $76.10   $76.10  
  Purchase #3 $226.28   4.571%   $236.6233   $236.62   $236.60   $236.60  
  Purchase #4 $169.54   6.764%   $181.0077   $181.01   $181.00   $181.00  
  Purchase #5 $114.68   5.157%   $120.594   $120.59   $120.60   $120.60  
  Purchase #6 $54.87   12.210%   $61.5696   $61.57   $61.55   $61.60  
  Purchase #7 $25.83   13.285%   $29.2615   $29.26   $29.25   $29.30  
  7 purchase totals = $709.78       $758.0699   $758.06   $758.00   $758.10