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	$22.89	6.167%	$24.3016	$24.30	$24.30	$24.30
Purchase #2	$150.46	3.526%	$155.7652	$155.77	$155.75	$155.80
Purchase #3	$249.34	11.463%	$277.9218	$277.92	$277.90	$277.90
Purchase #4	$77.57	6.790%	$82.837	$82.84	$82.85	$82.80
Purchase #5	$115.58	10.331%	$127.5206	$127.52	$127.50	$127.50
Purchase #6	$27.98	4.121%	$29.1331	$29.13	$29.15	$29.10
Purchase #7	$88.28	11.801%	$98.6979	$98.70	$98.70	$98.70
7 purchase totals =	$732.10		$796.1772	$796.18	$796.15	$796.10