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	$34.52	8.489%	$37.4504	$37.45	$37.45	$37.50
Purchase #2	$101.43	7.566%	$109.1042	$109.10	$109.10	$109.10
Purchase #3	$248.54	6.269%	$264.121	$264.12	$264.10	$264.10
Purchase #4	$120.66	9.142%	$131.6907	$131.69	$131.70	$131.70
Purchase #5	$18.71	11.280%	$20.8205	$20.82	$20.80	$20.80
Purchase #6	$133.92	10.415%	$147.8678	$147.87	$147.85	$147.90
Purchase #7	$91.29	5.865%	$96.6442	$96.64	$96.65	$96.60
7 purchase totals =	$749.07		$807.6988	$807.69	$807.65	$807.70