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 $177.99   11.434%   $198.3414   $198.34   $198.35   $198.30  
  Purchase #2 $211.72   12.297%   $237.7552   $237.76   $237.75   $237.80  
  Purchase #3 $174.39   10.283%   $192.3225   $192.32   $192.30   $192.30  
  Purchase #4 $231.83   5.782%   $245.2344   $245.23   $245.25   $245.20  
  Purchase #5 $5.44   7.120%   $5.8273   $5.83   $5.85   $5.80  
  Purchase #6 $76.92   6.318%   $81.7798   $81.78   $81.80   $81.80  
  Purchase #7 $45.80   11.230%   $50.9433   $50.94   $50.95   $50.90  
  7 purchase totals = $924.09       $1,012.2039   $1,012.20   $1,012.25   $1,012.10