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	$154.80	12.597%	$174.3002	$174.30	$174.30	$174.30
Purchase #2	$192.35	13.615%	$218.5385	$218.54	$218.55	$218.50
Purchase #3	$148.56	13.429%	$168.5101	$168.51	$168.50	$168.50
Purchase #4	$250.49	10.149%	$275.9122	$275.91	$275.90	$275.90
Purchase #5	$64.27	13.708%	$73.0801	$73.08	$73.10	$73.10
Purchase #6	$21.65	13.112%	$24.4887	$24.49	$24.50	$24.50
Purchase #7	$168.61	11.627%	$188.2143	$188.21	$188.20	$188.20
7 purchase totals =	$1,000.73		$1,123.0441	$1,123.04	$1,123.05	$1,123.00