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 $95.34   11.225%   $106.0419   $106.04   $106.05   $106.00  
  Purchase #2 $117.65   10.278%   $129.7421   $129.74   $129.75   $129.70  
  Purchase #3 $80.78   6.593%   $86.1058   $86.11   $86.10   $86.10  
  Purchase #4 $121.41   9.579%   $133.0399   $133.04   $133.05   $133.00  
  Purchase #5 $27.70   11.516%   $30.8899   $30.89   $30.90   $30.90  
  Purchase #6 $113.89   11.384%   $126.8552   $126.86   $126.85   $126.90  
  Purchase #7 $169.94   3.158%   $175.3067   $175.31   $175.30   $175.30  
  7 purchase totals = $726.71       $787.9815   $787.99   $788.00   $787.90