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	$99.93	4.177%	$104.1041	$104.10	$104.10	$104.10
Purchase #2	$79.83	8.648%	$86.7337	$86.73	$86.75	$86.70
Purchase #3	$77.53	4.352%	$80.9041	$80.90	$80.90	$80.90
Purchase #4	$61.42	5.200%	$64.6138	$64.61	$64.60	$64.60
Purchase #5	$41.29	11.134%	$45.8872	$45.89	$45.90	$45.90
Purchase #6	$168.46	6.774%	$179.8715	$179.87	$179.85	$179.90
Purchase #7	$74.92	3.763%	$77.7392	$77.74	$77.75	$77.70
7 purchase totals =	$603.38		$639.8536	$639.84	$639.85	$639.80