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	$95.44	8.841%	$103.8779	$103.88	$103.90	$103.90
Purchase #2	$223.34	7.834%	$240.8365	$240.84	$240.85	$240.80
Purchase #3	$32.82	13.554%	$37.2684	$37.27	$37.25	$37.30
Purchase #4	$51.90	4.249%	$54.1052	$54.11	$54.10	$54.10
Purchase #5	$41.29	13.435%	$46.8373	$46.84	$46.85	$46.80
Purchase #6	$132.97	13.863%	$151.4036	$151.40	$151.40	$151.40
Purchase #7	$52.42	12.489%	$58.9667	$58.97	$58.95	$59.00
7 purchase totals =	$630.18		$693.2956	$693.31	$693.30	$693.30