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	$42.35	11.254%	$47.1161	$47.12	$47.10	$47.10
Purchase #2	$209.89	11.190%	$233.3767	$233.38	$233.40	$233.40
Purchase #3	$46.64	8.489%	$50.5993	$50.60	$50.60	$50.60
Purchase #4	$10.27	9.105%	$11.2051	$11.21	$11.20	$11.20
Purchase #5	$129.97	7.224%	$139.359	$139.36	$139.35	$139.40
Purchase #6	$37.75	11.661%	$42.152	$42.15	$42.15	$42.20
Purchase #7	$190.66	12.293%	$214.0978	$214.10	$214.10	$214.10
7 purchase totals =	$667.53		$737.9060	$737.92	$737.90	$738.00