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	$157.87	6.345%	$167.8869	$167.89	$167.90	$167.90
Purchase #2	$37.74	11.455%	$42.0631	$42.06	$42.05	$42.10
Purchase #3	$21.28	6.258%	$22.6117	$22.61	$22.60	$22.60
Purchase #4	$30.46	8.736%	$33.121	$33.12	$33.10	$33.10
Purchase #5	$181.61	7.321%	$194.9057	$194.91	$194.90	$194.90
Purchase #6	$108.28	10.853%	$120.0316	$120.03	$120.05	$120.00
Purchase #7	$226.30	6.437%	$240.8669	$240.87	$240.85	$240.90
7 purchase totals =	$763.54		$821.4869	$821.49	$821.45	$821.50