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 $95.25   9.842%   $104.6245   $104.62   $104.60   $104.60  
  Purchase #2 $27.40   5.561%   $28.9237   $28.92   $28.90   $28.90  
  Purchase #3 $103.26   9.425%   $112.9923   $112.99   $113.00   $113.00  
  Purchase #4 $17.97   3.367%   $18.575   $18.58   $18.60   $18.60  
  Purchase #5 $8.33   12.450%   $9.3671   $9.37   $9.35   $9.40  
  Purchase #6 $32.53   10.840%   $36.0563   $36.06   $36.05   $36.10  
  Purchase #7 $54.29   6.200%   $57.656   $57.66   $57.65   $57.70  
  7 purchase totals = $339.03       $368.1949   $368.20   $368.15   $368.30