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	$191.75	8.674%	$208.3824	$208.38	$208.40	$208.40
Purchase #2	$55.33	4.229%	$57.6699	$57.67	$57.65	$57.70
Purchase #3	$250.41	5.604%	$264.443	$264.44	$264.45	$264.40
Purchase #4	$175.31	4.569%	$183.3199	$183.32	$183.30	$183.30
Purchase #5	$98.87	12.282%	$111.0132	$111.01	$111.00	$111.00
Purchase #6	$81.50	13.303%	$92.3419	$92.34	$92.35	$92.30
Purchase #7	$149.58	9.821%	$164.2703	$164.27	$164.25	$164.30
7 purchase totals =	$1,002.75		$1,081.4406	$1,081.43	$1,081.40	$1,081.40