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	$138.40	6.583%	$147.5109	$147.51	$147.50	$147.50
Purchase #2	$154.73	13.353%	$175.3911	$175.39	$175.40	$175.40
Purchase #3	$114.30	12.225%	$128.2732	$128.27	$128.25	$128.30
Purchase #4	$206.55	4.525%	$215.8964	$215.90	$215.90	$215.90
Purchase #5	$154.48	5.464%	$162.9208	$162.92	$162.90	$162.90
Purchase #6	$246.31	8.747%	$267.8547	$267.85	$267.85	$267.90
Purchase #7	$153.50	13.684%	$174.5049	$174.50	$174.50	$174.50
7 purchase totals =	$1,168.27		$1,272.3520	$1,272.34	$1,272.30	$1,272.40