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 $182.37   10.188%   $200.9499   $200.95   $200.95   $200.90  
  Purchase #2 $47.50   13.594%   $53.9572   $53.96   $53.95   $54.00  
  Purchase #3 $176.56   7.455%   $189.7225   $189.72   $189.70   $189.70  
  Purchase #4 $51.87   3.254%   $53.5578   $53.56   $53.55   $53.60  
  Purchase #5 $64.96   5.512%   $68.5406   $68.54   $68.55   $68.50  
  Purchase #6 $70.81   7.488%   $76.1123   $76.11   $76.10   $76.10  
  Purchase #7 $246.57   7.710%   $265.5805   $265.58   $265.60   $265.60  
  7 purchase totals = $840.64       $908.4208   $908.42   $908.40   $908.40