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	$99.78	3.231%	$103.0039	$103.00	$103.00	$103.00
Purchase #2	$151.51	9.369%	$165.705	$165.71	$165.70	$165.70
Purchase #3	$67.85	13.656%	$77.1156	$77.12	$77.10	$77.10
Purchase #4	$74.60	5.544%	$78.7358	$78.74	$78.75	$78.70
Purchase #5	$74.76	3.112%	$77.0865	$77.09	$77.10	$77.10
Purchase #6	$188.96	11.564%	$210.8113	$210.81	$210.80	$210.80
Purchase #7	$49.64	8.735%	$53.9761	$53.98	$54.00	$54.00
7 purchase totals =	$707.10		$766.4342	$766.45	$766.45	$766.40