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	$100.69	3.142%	$103.8537	$103.85	$103.85	$103.90
Purchase #2	$101.33	8.472%	$109.9147	$109.91	$109.90	$109.90
Purchase #3	$39.69	10.830%	$43.9884	$43.99	$44.00	$44.00
Purchase #4	$73.37	13.380%	$83.1869	$83.19	$83.20	$83.20
Purchase #5	$64.39	13.114%	$72.8341	$72.83	$72.85	$72.80
Purchase #6	$103.68	4.638%	$108.4887	$108.49	$108.50	$108.50
Purchase #7	$28.38	11.192%	$31.5563	$31.56	$31.55	$31.60
7 purchase totals =	$511.53		$553.8228	$553.82	$553.85	$553.90