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 $10.62   4.544%   $11.1026   $11.10   $11.10   $11.10  
  Purchase #2 $216.83   3.193%   $223.7534   $223.75   $223.75   $223.80  
  Purchase #3 $195.70   13.354%   $221.8338   $221.83   $221.85   $221.80  
  Purchase #4 $152.75   11.224%   $169.8947   $169.89   $169.90   $169.90  
  Purchase #5 $194.26   9.643%   $212.9925   $212.99   $213.00   $213.00  
  Purchase #6 $15.25   10.396%   $16.8354   $16.84   $16.85   $16.80  
  Purchase #7 $56.90   5.102%   $59.803   $59.80   $59.80   $59.80  
  7 purchase totals = $842.31       $916.2154   $916.20   $916.25   $916.20