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	$164.49	12.396%	$184.8802	$184.88	$184.90	$184.90
Purchase #2	$227.52	5.680%	$240.4431	$240.44	$240.45	$240.40
Purchase #3	$78.92	4.708%	$82.6356	$82.64	$82.65	$82.60
Purchase #4	$29.81	13.552%	$33.8499	$33.85	$33.85	$33.80
Purchase #5	$72.50	9.739%	$79.5608	$79.56	$79.55	$79.60
Purchase #6	$237.89	5.197%	$250.2531	$250.25	$250.25	$250.30
Purchase #7	$78.71	13.129%	$89.0438	$89.04	$89.05	$89.00
7 purchase totals =	$889.84		$960.6665	$960.66	$960.70	$960.60