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	$138.66	9.469%	$151.7897	$151.79	$151.80	$151.80
Purchase #2	$94.40	10.330%	$104.1515	$104.15	$104.15	$104.20
Purchase #3	$36.34	12.537%	$40.8959	$40.90	$40.90	$40.90
Purchase #4	$215.33	12.809%	$242.9116	$242.91	$242.90	$242.90
Purchase #5	$161.76	6.166%	$171.7341	$171.73	$171.75	$171.70
Purchase #6	$183.95	11.622%	$205.3287	$205.33	$205.35	$205.30
Purchase #7	$77.98	5.518%	$82.2829	$82.28	$82.30	$82.30
7 purchase totals =	$908.42		$999.0944	$999.09	$999.15	$999.10