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	$136.67	6.217%	$145.1668	$145.17	$145.15	$145.20
Purchase #2	$36.93	11.331%	$41.1145	$41.11	$41.10	$41.10
Purchase #3	$124.45	10.394%	$137.3853	$137.39	$137.40	$137.40
Purchase #4	$33.83	11.861%	$37.8426	$37.84	$37.85	$37.80
Purchase #5	$145.28	4.441%	$151.7319	$151.73	$151.75	$151.70
Purchase #6	$96.68	12.808%	$109.0628	$109.06	$109.05	$109.10
Purchase #7	$135.28	6.126%	$143.5673	$143.57	$143.55	$143.60
7 purchase totals =	$709.12		$765.8712	$765.87	$765.85	$765.90