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 $190.65   13.256%   $215.9226   $215.92   $215.90   $215.90  
  Purchase #2 $151.41   9.221%   $165.3715   $165.37   $165.35   $165.40  
  Purchase #3 $121.64   10.814%   $134.7941   $134.79   $134.80   $134.80  
  Purchase #4 $190.79   3.448%   $197.3684   $197.37   $197.35   $197.40  
  Purchase #5 $62.26   8.649%   $67.6449   $67.64   $67.65   $67.60  
  Purchase #6 $151.27   6.443%   $161.0163   $161.02   $161.00   $161.00  
  Purchase #7 $100.69   6.419%   $107.1533   $107.15   $107.15   $107.20  
  7 purchase totals = $968.71       $1,049.2711   $1,049.26   $1,049.20   $1,049.30