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	$86.63	4.203%	$90.2711	$90.27	$90.25	$90.30
Purchase #2	$128.67	13.483%	$146.0186	$146.02	$146.00	$146.00
Purchase #3	$91.87	3.478%	$95.0652	$95.07	$95.05	$95.10
Purchase #4	$122.91	9.279%	$134.3148	$134.31	$134.30	$134.30
Purchase #5	$107.88	11.224%	$119.9885	$119.99	$120.00	$120.00
Purchase #6	$94.88	11.474%	$105.7665	$105.77	$105.75	$105.80
Purchase #7	$84.82	6.260%	$90.1297	$90.13	$90.15	$90.10
7 purchase totals =	$717.66		$781.5544	$781.56	$781.50	$781.60