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 $182.45   13.777%   $207.5861   $207.59   $207.60   $207.60  
  Purchase #2 $189.60   5.821%   $200.6366   $200.64   $200.65   $200.60  
  Purchase #3 $22.25   12.214%   $24.9676   $24.97   $24.95   $25.00  
  Purchase #4 $214.34   13.279%   $242.8022   $242.80   $242.80   $242.80  
  Purchase #5 $45.35   12.297%   $50.9267   $50.93   $50.95   $50.90  
  Purchase #6 $5.77   6.768%   $6.1605   $6.16   $6.15   $6.20  
  Purchase #7 $53.97   12.179%   $60.543   $60.54   $60.55   $60.50  
  7 purchase totals = $713.73       $793.6227   $793.63   $793.65   $793.60