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	$107.30	8.600%	$116.5278	$116.53	$116.55	$116.50
Purchase #2	$180.40	11.124%	$200.4677	$200.47	$200.45	$200.50
Purchase #3	$91.63	8.781%	$99.676	$99.68	$99.70	$99.70
Purchase #4	$95.68	8.779%	$104.0797	$104.08	$104.10	$104.10
Purchase #5	$5.72	13.868%	$6.5132	$6.51	$6.50	$6.50
Purchase #6	$218.92	9.130%	$238.9074	$238.91	$238.90	$238.90
Purchase #7	$88.33	12.707%	$99.5541	$99.55	$99.55	$99.60
7 purchase totals =	$787.98		$865.7259	$865.73	$865.75	$865.80