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	$100.26	8.121%	$108.4021	$108.40	$108.40	$108.40
Purchase #2	$170.91	7.408%	$183.571	$183.57	$183.55	$183.60
Purchase #3	$77.64	10.598%	$85.8683	$85.87	$85.85	$85.90
Purchase #4	$123.71	9.377%	$135.3103	$135.31	$135.30	$135.30
Purchase #5	$62.89	7.327%	$67.498	$67.50	$67.50	$67.50
Purchase #6	$30.46	9.341%	$33.3053	$33.31	$33.30	$33.30
Purchase #7	$172.57	3.619%	$178.8153	$178.82	$178.80	$178.80
7 purchase totals =	$738.44		$792.7703	$792.78	$792.70	$792.80