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	$149.47	3.294%	$154.3935	$154.39	$154.40	$154.40
Purchase #2	$89.39	10.281%	$98.5802	$98.58	$98.60	$98.60
Purchase #3	$13.84	10.436%	$15.2843	$15.28	$15.30	$15.30
Purchase #4	$61.88	13.794%	$70.4157	$70.42	$70.40	$70.40
Purchase #5	$100.73	4.129%	$104.8891	$104.89	$104.90	$104.90
Purchase #6	$59.67	9.626%	$65.4138	$65.41	$65.40	$65.40
Purchase #7	$41.62	10.283%	$45.8998	$45.90	$45.90	$45.90
7 purchase totals =	$516.60		$554.8764	$554.87	$554.90	$554.90