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	$124.86	11.357%	$139.0404	$139.04	$139.05	$139.00
Purchase #2	$237.91	12.529%	$267.7177	$267.72	$267.70	$267.70
Purchase #3	$30.36	11.555%	$33.8681	$33.87	$33.85	$33.90
Purchase #4	$249.53	9.472%	$273.1655	$273.17	$273.15	$273.20
Purchase #5	$192.29	12.419%	$216.1705	$216.17	$216.15	$216.20
Purchase #6	$56.68	10.118%	$62.4149	$62.41	$62.40	$62.40
Purchase #7	$37.78	10.867%	$41.8856	$41.89	$41.90	$41.90
7 purchase totals =	$929.41		$1,034.2627	$1,034.27	$1,034.20	$1,034.30