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 $87.86   10.337%   $96.9421   $96.94   $96.95   $96.90  
  Purchase #2 $213.69   5.463%   $225.3639   $225.36   $225.35   $225.40  
  Purchase #3 $39.25   5.839%   $41.5418   $41.54   $41.55   $41.50  
  Purchase #4 $114.26   13.289%   $129.444   $129.44   $129.45   $129.40  
  Purchase #5 $64.79   4.254%   $67.5462   $67.55   $67.55   $67.50  
  Purchase #6 $24.85   3.544%   $25.7307   $25.73   $25.75   $25.70  
  Purchase #7 $21.55   9.273%   $23.5483   $23.55   $23.55   $23.50  
  7 purchase totals = $566.25       $610.1170   $610.11   $610.15   $609.90