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	$18.86	3.195%	$19.4626	$19.46	$19.45	$19.50
Purchase #2	$240.86	12.478%	$270.9145	$270.91	$270.90	$270.90
Purchase #3	$112.93	12.786%	$127.3692	$127.37	$127.35	$127.40
Purchase #4	$206.56	12.502%	$232.3841	$232.38	$232.40	$232.40
Purchase #5	$19.98	6.801%	$21.3388	$21.34	$21.35	$21.30
Purchase #6	$11.52	11.536%	$12.8489	$12.85	$12.85	$12.80
Purchase #7	$130.77	10.551%	$144.5675	$144.57	$144.55	$144.60
7 purchase totals =	$741.48		$828.8856	$828.88	$828.85	$828.90