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	$26.80	7.685%	$28.8596	$28.86	$28.85	$28.90
Purchase #2	$127.91	12.788%	$144.2671	$144.27	$144.25	$144.30
Purchase #3	$195.41	11.707%	$218.2866	$218.29	$218.30	$218.30
Purchase #4	$63.86	9.545%	$69.9554	$69.96	$69.95	$70.00
Purchase #5	$96.59	5.477%	$101.8802	$101.88	$101.90	$101.90
Purchase #6	$154.64	6.811%	$165.1725	$165.17	$165.15	$165.20
Purchase #7	$94.59	11.336%	$105.3127	$105.31	$105.30	$105.30
7 purchase totals =	$759.80		$833.7341	$833.74	$833.70	$833.90