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	$60.92	7.753%	$65.6431	$65.64	$65.65	$65.60
Purchase #2	$38.38	7.686%	$41.3299	$41.33	$41.35	$41.30
Purchase #3	$130.56	13.540%	$148.2378	$148.24	$148.25	$148.20
Purchase #4	$99.30	4.809%	$104.0753	$104.08	$104.10	$104.10
Purchase #5	$100.76	5.694%	$106.4973	$106.50	$106.50	$106.50
Purchase #6	$144.62	3.817%	$150.1401	$150.14	$150.15	$150.10
Purchase #7	$45.84	13.502%	$52.0293	$52.03	$52.05	$52.00
7 purchase totals =	$620.38		$667.9528	$667.96	$668.05	$667.80