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	$161.39	11.697%	$180.2678	$180.27	$180.25	$180.30
Purchase #2	$42.38	11.113%	$47.0897	$47.09	$47.10	$47.10
Purchase #3	$180.73	10.811%	$200.2687	$200.27	$200.25	$200.30
Purchase #4	$21.51	4.577%	$22.4945	$22.49	$22.50	$22.50
Purchase #5	$32.67	10.631%	$36.1431	$36.14	$36.15	$36.10
Purchase #6	$83.48	3.326%	$86.2565	$86.26	$86.25	$86.30
Purchase #7	$151.47	3.183%	$156.2913	$156.29	$156.30	$156.30
7 purchase totals =	$673.63		$728.8116	$728.81	$728.80	$728.90