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	$213.91	4.588%	$223.7242	$223.72	$223.70	$223.70
Purchase #2	$39.89	7.519%	$42.8893	$42.89	$42.90	$42.90
Purchase #3	$186.97	12.238%	$209.8514	$209.85	$209.85	$209.90
Purchase #4	$226.42	9.402%	$247.708	$247.71	$247.70	$247.70
Purchase #5	$62.80	7.525%	$67.5257	$67.53	$67.55	$67.50
Purchase #6	$60.25	3.734%	$62.4997	$62.50	$62.50	$62.50
Purchase #7	$216.66	13.578%	$246.0781	$246.08	$246.10	$246.10
7 purchase totals =	$1,006.90		$1,100.2764	$1,100.28	$1,100.30	$1,100.30