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 $67.64   13.609%   $76.8451   $76.85   $76.85   $76.80  
  Purchase #2 $46.71   11.743%   $52.1952   $52.20   $52.20   $52.20  
  Purchase #3 $250.64   7.382%   $269.1422   $269.14   $269.15   $269.10  
  Purchase #4 $67.62   10.305%   $74.5882   $74.59   $74.60   $74.60  
  Purchase #5 $13.29   13.307%   $15.0585   $15.06   $15.05   $15.10  
  Purchase #6 $198.75   11.359%   $221.326   $221.33   $221.35   $221.30  
  Purchase #7 $78.79   3.552%   $81.5886   $81.59   $81.60   $81.60  
  7 purchase totals = $723.44       $790.7438   $790.76   $790.80   $790.70