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	$34.67	11.371%	$38.6123	$38.61	$38.60	$38.60
Purchase #2	$42.98	13.809%	$48.9151	$48.92	$48.90	$48.90
Purchase #3	$186.52	12.475%	$209.7884	$209.79	$209.80	$209.80
Purchase #4	$82.48	12.627%	$92.8947	$92.89	$92.90	$92.90
Purchase #5	$175.33	8.539%	$190.3014	$190.30	$190.30	$190.30
Purchase #6	$176.63	4.563%	$184.6896	$184.69	$184.70	$184.70
Purchase #7	$223.65	10.592%	$247.339	$247.34	$247.35	$247.30
7 purchase totals =	$922.26		$1,012.5405	$1,012.54	$1,012.55	$1,012.50