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 $72.31   6.294%   $76.8612   $76.86   $76.85   $76.90  
  Purchase #2 $107.43   5.724%   $113.5793   $113.58   $113.60   $113.60  
  Purchase #3 $67.85   11.419%   $75.5978   $75.60   $75.60   $75.60  
  Purchase #4 $123.82   8.195%   $133.967   $133.97   $133.95   $134.00  
  Purchase #5 $218.33   13.867%   $248.6058   $248.61   $248.60   $248.60  
  Purchase #6 $54.87   10.851%   $60.8239   $60.82   $60.80   $60.80  
  Purchase #7 $68.97   12.356%   $77.4919   $77.49   $77.50   $77.50  
  7 purchase totals = $713.58       $786.9269   $786.93   $786.90   $787.00