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	$18.28	10.104%	$20.127	$20.13	$20.15	$20.10
Purchase #2	$116.31	9.539%	$127.4048	$127.40	$127.40	$127.40
Purchase #3	$98.26	6.756%	$104.8984	$104.90	$104.90	$104.90
Purchase #4	$30.57	12.132%	$34.2788	$34.28	$34.30	$34.30
Purchase #5	$210.81	9.769%	$231.404	$231.40	$231.40	$231.40
Purchase #6	$39.64	6.688%	$42.2911	$42.29	$42.30	$42.30
Purchase #7	$150.78	12.437%	$169.5325	$169.53	$169.55	$169.50
7 purchase totals =	$664.65		$729.9366	$729.93	$730.00	$729.90