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 $162.61   9.618%   $178.2498   $178.25   $178.25   $178.20  
  Purchase #2 $84.68   10.649%   $93.6976   $93.70   $93.70   $93.70  
  Purchase #3 $155.46   7.621%   $167.3076   $167.31   $167.30   $167.30  
  Purchase #4 $57.69   4.760%   $60.436   $60.44   $60.45   $60.40  
  Purchase #5 $192.60   10.628%   $213.0695   $213.07   $213.05   $213.10  
  Purchase #6 $74.85   5.285%   $78.8058   $78.81   $78.80   $78.80  
  Purchase #7 $225.56   4.606%   $235.9493   $235.95   $235.95   $235.90  
  7 purchase totals = $953.45       $1,027.5156   $1,027.53   $1,027.50   $1,027.40