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	$213.32	13.513%	$242.1459	$242.15	$242.15	$242.10
Purchase #2	$150.30	3.522%	$155.5936	$155.59	$155.60	$155.60
Purchase #3	$141.27	3.541%	$146.2724	$146.27	$146.25	$146.30
Purchase #4	$100.83	3.870%	$104.7321	$104.73	$104.75	$104.70
Purchase #5	$100.92	13.803%	$114.85	$114.85	$114.85	$114.90
Purchase #6	$117.61	11.596%	$131.2481	$131.25	$131.25	$131.20
Purchase #7	$103.48	4.494%	$108.1304	$108.13	$108.15	$108.10
7 purchase totals =	$927.73		$1,002.9725	$1,002.97	$1,003.00	$1,002.90