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 $232.29   6.626%   $247.6815   $247.68   $247.70   $247.70  
  Purchase #2 $24.75   5.268%   $26.0538   $26.05   $26.05   $26.10  
  Purchase #3 $60.62   6.346%   $64.4669   $64.47   $64.45   $64.50  
  Purchase #4 $39.93   9.635%   $43.7773   $43.78   $43.80   $43.80  
  Purchase #5 $52.85   10.568%   $58.4352   $58.44   $58.45   $58.40  
  Purchase #6 $67.40   13.384%   $76.4208   $76.42   $76.40   $76.40  
  Purchase #7 $208.36   5.466%   $219.749   $219.75   $219.75   $219.70  
  7 purchase totals = $686.20       $736.5845   $736.59   $736.60   $736.60