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	$97.78	3.136%	$100.8464	$100.85	$100.85	$100.80
Purchase #2	$95.69	6.476%	$101.8869	$101.89	$101.90	$101.90
Purchase #3	$26.54	3.488%	$27.4657	$27.47	$27.45	$27.50
Purchase #4	$242.83	9.448%	$265.7726	$265.77	$265.75	$265.80
Purchase #5	$95.31	4.643%	$99.7352	$99.74	$99.75	$99.70
Purchase #6	$23.67	8.267%	$25.6268	$25.63	$25.65	$25.60
Purchase #7	$236.81	13.780%	$269.4424	$269.44	$269.45	$269.40
7 purchase totals =	$818.63		$890.7760	$890.79	$890.80	$890.70