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	$59.43	3.672%	$61.6123	$61.61	$61.60	$61.60
Purchase #2	$20.31	7.524%	$21.8381	$21.84	$21.85	$21.80
Purchase #3	$210.88	12.865%	$238.0097	$238.01	$238.00	$238.00
Purchase #4	$29.98	7.851%	$32.3337	$32.33	$32.35	$32.30
Purchase #5	$191.85	13.257%	$217.2836	$217.28	$217.30	$217.30
Purchase #6	$51.26	11.695%	$57.2549	$57.25	$57.25	$57.30
Purchase #7	$98.72	10.475%	$109.0609	$109.06	$109.05	$109.10
7 purchase totals =	$662.43		$737.3932	$737.38	$737.40	$737.40