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 $186.32   7.737%   $200.7356   $200.74   $200.75   $200.70  
  Purchase #2 $85.99   9.859%   $94.4678   $94.47   $94.45   $94.50  
  Purchase #3 $178.97   9.490%   $195.9543   $195.95   $195.95   $196.00  
  Purchase #4 $41.88   12.192%   $46.986   $46.99   $47.00   $47.00  
  Purchase #5 $195.43   7.416%   $209.9231   $209.92   $209.90   $209.90  
  Purchase #6 $52.34   6.371%   $55.6746   $55.67   $55.65   $55.70  
  Purchase #7 $208.86   8.297%   $226.1891   $226.19   $226.20   $226.20  
  7 purchase totals = $949.79       $1,029.9305   $1,029.93   $1,029.90   $1,030.00