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	$95.63	4.825%	$100.2441	$100.24	$100.25	$100.20
Purchase #2	$234.63	8.748%	$255.1554	$255.16	$255.15	$255.20
Purchase #3	$139.32	11.315%	$155.0841	$155.08	$155.10	$155.10
Purchase #4	$34.51	6.614%	$36.7925	$36.79	$36.80	$36.80
Purchase #5	$36.29	7.820%	$39.1279	$39.13	$39.15	$39.10
Purchase #6	$149.26	4.437%	$155.8827	$155.88	$155.90	$155.90
Purchase #7	$39.34	3.651%	$40.7763	$40.78	$40.80	$40.80
7 purchase totals =	$728.98		$783.0630	$783.06	$783.15	$783.10