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	$169.83	11.223%	$188.89	$188.89	$188.90	$188.90
Purchase #2	$209.32	10.315%	$230.9114	$230.91	$230.90	$230.90
Purchase #3	$130.67	9.377%	$142.9229	$142.92	$142.90	$142.90
Purchase #4	$82.41	5.318%	$86.7926	$86.79	$86.80	$86.80
Purchase #5	$58.97	11.813%	$65.9361	$65.94	$65.95	$65.90
Purchase #6	$210.55	8.425%	$228.2888	$228.29	$228.30	$228.30
Purchase #7	$216.85	11.478%	$241.74	$241.74	$241.75	$241.70
7 purchase totals =	$1,078.60		$1,185.4818	$1,185.48	$1,185.50	$1,185.40