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	$238.53	12.624%	$268.642	$268.64	$268.65	$268.60
Purchase #2	$203.85	12.178%	$228.6749	$228.67	$228.65	$228.70
Purchase #3	$162.78	11.117%	$180.8763	$180.88	$180.90	$180.90
Purchase #4	$58.72	12.193%	$65.8797	$65.88	$65.90	$65.90
Purchase #5	$202.50	6.772%	$216.2133	$216.21	$216.20	$216.20
Purchase #6	$161.62	6.593%	$172.2756	$172.28	$172.30	$172.30
Purchase #7	$85.56	11.393%	$95.3079	$95.31	$95.30	$95.30
7 purchase totals =	$1,113.56		$1,227.8697	$1,227.87	$1,227.90	$1,227.90