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	$51.54	6.557%	$54.9195	$54.92	$54.90	$54.90
Purchase #2	$31.66	9.175%	$34.5648	$34.56	$34.55	$34.60
Purchase #3	$94.89	4.661%	$99.3128	$99.31	$99.30	$99.30
Purchase #4	$189.98	7.604%	$204.4261	$204.43	$204.45	$204.40
Purchase #5	$204.76	11.469%	$228.2439	$228.24	$228.25	$228.20
Purchase #6	$87.97	3.825%	$91.3349	$91.33	$91.35	$91.30
Purchase #7	$14.59	6.714%	$15.5696	$15.57	$15.55	$15.60
7 purchase totals =	$675.39		$728.3716	$728.36	$728.35	$728.30