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	$149.92	9.597%	$164.3078	$164.31	$164.30	$164.30
Purchase #2	$46.36	12.641%	$52.2204	$52.22	$52.20	$52.20
Purchase #3	$149.86	10.329%	$165.339	$165.34	$165.35	$165.30
Purchase #4	$82.83	10.674%	$91.6713	$91.67	$91.65	$91.70
Purchase #5	$64.38	9.587%	$70.5521	$70.55	$70.55	$70.60
Purchase #6	$90.65	11.327%	$100.9179	$100.92	$100.90	$100.90
Purchase #7	$13.49	4.747%	$14.1304	$14.13	$14.15	$14.10
7 purchase totals =	$597.49		$659.1389	$659.14	$659.10	$659.10