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 $125.93   13.532%   $142.9708   $142.97   $142.95   $143.00  
  Purchase #2 $246.74   5.202%   $259.5754   $259.58   $259.60   $259.60  
  Purchase #3 $68.36   11.158%   $75.9876   $75.99   $76.00   $76.00  
  Purchase #4 $233.41   6.254%   $248.0075   $248.01   $248.00   $248.00  
  Purchase #5 $47.78   9.643%   $52.3874   $52.39   $52.40   $52.40  
  Purchase #6 $96.89   13.145%   $109.6262   $109.63   $109.65   $109.60  
  Purchase #7 $123.87   8.345%   $134.207   $134.21   $134.20   $134.20  
  7 purchase totals = $942.98       $1,022.7619   $1,022.78   $1,022.80   $1,022.80