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	$169.58	9.234%	$185.239	$185.24	$185.25	$185.20
Purchase #2	$49.38	10.809%	$54.7175	$54.72	$54.70	$54.70
Purchase #3	$143.67	4.788%	$150.5489	$150.55	$150.55	$150.50
Purchase #4	$101.54	11.796%	$113.5177	$113.52	$113.50	$113.50
Purchase #5	$90.31	10.621%	$99.9018	$99.90	$99.90	$99.90
Purchase #6	$227.92	5.373%	$240.1661	$240.17	$240.15	$240.20
Purchase #7	$60.89	10.319%	$67.1732	$67.17	$67.15	$67.20
7 purchase totals =	$843.29		$911.2642	$911.27	$911.20	$911.20