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	$36.76	7.364%	$39.467	$39.47	$39.45	$39.50
Purchase #2	$65.29	9.852%	$71.7224	$71.72	$71.70	$71.70
Purchase #3	$124.93	12.276%	$140.2664	$140.27	$140.25	$140.30
Purchase #4	$55.63	6.609%	$59.3066	$59.31	$59.30	$59.30
Purchase #5	$196.92	6.426%	$209.5741	$209.57	$209.55	$209.60
Purchase #6	$169.88	13.504%	$192.8206	$192.82	$192.80	$192.80
Purchase #7	$215.66	5.501%	$227.5235	$227.52	$227.50	$227.50
7 purchase totals =	$865.07		$940.6806	$940.68	$940.55	$940.70