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	$224.58	13.868%	$255.7248	$255.72	$255.70	$255.70
Purchase #2	$127.86	11.744%	$142.8759	$142.88	$142.90	$142.90
Purchase #3	$73.32	12.219%	$82.279	$82.28	$82.30	$82.30
Purchase #4	$65.50	10.654%	$72.4784	$72.48	$72.50	$72.50
Purchase #5	$249.41	11.515%	$278.1296	$278.13	$278.15	$278.10
Purchase #6	$180.39	9.753%	$197.9834	$197.98	$198.00	$198.00
Purchase #7	$192.60	9.412%	$210.7275	$210.73	$210.75	$210.70
7 purchase totals =	$1,113.66		$1,240.1986	$1,240.20	$1,240.30	$1,240.20