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	$104.38	12.641%	$117.5747	$117.57	$117.55	$117.60
Purchase #2	$77.95	6.413%	$82.9489	$82.95	$82.95	$82.90
Purchase #3	$137.47	11.598%	$153.4138	$153.41	$153.40	$153.40
Purchase #4	$122.26	4.625%	$127.9145	$127.91	$127.90	$127.90
Purchase #5	$245.87	13.804%	$279.8099	$279.81	$279.80	$279.80
Purchase #6	$56.29	12.376%	$63.2565	$63.26	$63.25	$63.30
Purchase #7	$125.61	4.312%	$131.0263	$131.03	$131.05	$131.00
7 purchase totals =	$869.83		$955.9446	$955.94	$955.90	$955.90