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	$111.45	8.393%	$120.804	$120.80	$120.80	$120.80
Purchase #2	$209.50	13.674%	$238.147	$238.15	$238.15	$238.10
Purchase #3	$144.67	5.637%	$152.825	$152.83	$152.85	$152.80
Purchase #4	$171.88	7.385%	$184.5733	$184.57	$184.55	$184.60
Purchase #5	$163.54	11.192%	$181.8434	$181.84	$181.85	$181.80
Purchase #6	$85.52	13.378%	$96.9609	$96.96	$96.95	$97.00
Purchase #7	$101.76	4.334%	$106.1703	$106.17	$106.15	$106.20
7 purchase totals =	$988.32		$1,081.3239	$1,081.32	$1,081.30	$1,081.30