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	$163.55	6.669%	$174.4571	$174.46	$174.45	$174.50
Purchase #2	$196.49	4.740%	$205.8036	$205.80	$205.80	$205.80
Purchase #3	$135.80	9.443%	$148.6236	$148.62	$148.60	$148.60
Purchase #4	$210.92	8.430%	$228.7006	$228.70	$228.70	$228.70
Purchase #5	$109.87	9.632%	$120.4527	$120.45	$120.45	$120.50
Purchase #6	$160.34	6.847%	$171.3185	$171.32	$171.30	$171.30
Purchase #7	$230.89	8.774%	$251.1483	$251.15	$251.15	$251.10
7 purchase totals =	$1,207.86		$1,300.5044	$1,300.50	$1,300.45	$1,300.50