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	$81.63	9.626%	$89.4877	$89.49	$89.50	$89.50
Purchase #2	$156.51	10.481%	$172.9138	$172.91	$172.90	$172.90
Purchase #3	$22.64	3.566%	$23.4473	$23.45	$23.45	$23.40
Purchase #4	$238.88	4.680%	$250.0596	$250.06	$250.05	$250.10
Purchase #5	$124.87	9.105%	$136.2394	$136.24	$136.25	$136.20
Purchase #6	$218.73	11.132%	$243.079	$243.08	$243.10	$243.10
Purchase #7	$162.52	13.728%	$184.8307	$184.83	$184.85	$184.80
7 purchase totals =	$1,005.78		$1,100.0575	$1,100.06	$1,100.10	$1,100.00