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	$32.99	3.293%	$34.0764	$34.08	$34.10	$34.10
Purchase #2	$115.51	13.581%	$131.1974	$131.20	$131.20	$131.20
Purchase #3	$56.89	7.764%	$61.3069	$61.31	$61.30	$61.30
Purchase #4	$93.56	7.535%	$100.6097	$100.61	$100.60	$100.60
Purchase #5	$116.40	11.173%	$129.4054	$129.41	$129.40	$129.40
Purchase #6	$41.34	4.815%	$43.3305	$43.33	$43.35	$43.30
Purchase #7	$22.60	12.207%	$25.3588	$25.36	$25.35	$25.40
7 purchase totals =	$479.29		$525.2851	$525.30	$525.30	$525.30