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 $72.58   4.752%   $76.029   $76.03   $76.05   $76.00  
  Purchase #2 $79.97   5.221%   $84.1452   $84.15   $84.15   $84.10  
  Purchase #3 $217.75   5.773%   $230.3207   $230.32   $230.30   $230.30  
  Purchase #4 $157.79   11.405%   $175.7859   $175.79   $175.80   $175.80  
  Purchase #5 $95.84   11.120%   $106.4974   $106.50   $106.50   $106.50  
  Purchase #6 $147.65   5.578%   $155.8859   $155.89   $155.90   $155.90  
  Purchase #7 $106.93   7.256%   $114.6888   $114.69   $114.70   $114.70  
  7 purchase totals = $878.51       $943.3529   $943.37   $943.40   $943.30