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 $114.97   13.267%   $130.2231   $130.22   $130.20   $130.20  
  Purchase #2 $118.47   3.552%   $122.6781   $122.68   $122.70   $122.70  
  Purchase #3 $121.93   3.615%   $126.3378   $126.34   $126.35   $126.30  
  Purchase #4 $117.59   3.326%   $121.501   $121.50   $121.50   $121.50  
  Purchase #5 $142.27   5.305%   $149.8174   $149.82   $149.80   $149.80  
  Purchase #6 $71.63   5.615%   $75.652   $75.65   $75.65   $75.70  
  Purchase #7 $244.43   9.311%   $267.1889   $267.19   $267.20   $267.20  
  7 purchase totals = $931.29       $993.3983   $993.40   $993.40   $993.40