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	$131.43	11.138%	$146.0687	$146.07	$146.05	$146.10
Purchase #2	$103.55	12.722%	$116.7236	$116.72	$116.70	$116.70
Purchase #3	$122.37	12.363%	$137.4986	$137.50	$137.50	$137.50
Purchase #4	$204.79	7.588%	$220.3295	$220.33	$220.35	$220.30
Purchase #5	$212.25	13.363%	$240.613	$240.61	$240.60	$240.60
Purchase #6	$198.56	10.589%	$219.5855	$219.59	$219.60	$219.60
Purchase #7	$17.84	12.477%	$20.0659	$20.07	$20.05	$20.10
7 purchase totals =	$990.79		$1,100.8848	$1,100.89	$1,100.85	$1,100.90