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 $242.41   10.142%   $266.9952   $267.00   $267.00   $267.00  
  Purchase #2 $121.65   8.451%   $131.9306   $131.93   $131.95   $131.90  
  Purchase #3 $38.99   4.542%   $40.7609   $40.76   $40.75   $40.80  
  Purchase #4 $56.85   5.461%   $59.9546   $59.95   $59.95   $60.00  
  Purchase #5 $223.52   6.240%   $237.4676   $237.47   $237.45   $237.50  
  Purchase #6 $186.82   13.196%   $211.4728   $211.47   $211.45   $211.50  
  Purchase #7 $12.50   8.444%   $13.5555   $13.56   $13.55   $13.60  
  7 purchase totals = $882.74       $962.1372   $962.14   $962.10   $962.30