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 $201.55   3.178%   $207.9553   $207.96   $207.95   $208.00  
  Purchase #2 $70.42   3.659%   $72.9967   $73.00   $73.00   $73.00  
  Purchase #3 $246.90   8.247%   $267.2618   $267.26   $267.25   $267.30  
  Purchase #4 $199.39   7.374%   $214.093   $214.09   $214.10   $214.10  
  Purchase #5 $68.62   8.500%   $74.4527   $74.45   $74.45   $74.50  
  Purchase #6 $222.96   6.543%   $237.5483   $237.55   $237.55   $237.50  
  Purchase #7 $118.74   8.355%   $128.6607   $128.66   $128.65   $128.70  
  7 purchase totals = $1,128.58       $1,202.9685   $1,202.97   $1,202.95   $1,203.10