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 $199.95   5.620%   $211.1872   $211.19   $211.20   $211.20  
  Purchase #2 $220.61   3.163%   $227.5879   $227.59   $227.60   $227.60  
  Purchase #3 $115.95   7.599%   $124.761   $124.76   $124.75   $124.80  
  Purchase #4 $67.33   8.313%   $72.9271   $72.93   $72.95   $72.90  
  Purchase #5 $94.56   3.844%   $98.1949   $98.19   $98.20   $98.20  
  Purchase #6 $169.68   11.691%   $189.5173   $189.52   $189.50   $189.50  
  Purchase #7 $151.28   3.286%   $156.2511   $156.25   $156.25   $156.30  
  7 purchase totals = $1,019.36       $1,080.4265   $1,080.43   $1,080.45   $1,080.50