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	$33.76	4.146%	$35.1597	$35.16	$35.15	$35.20
Purchase #2	$39.38	7.352%	$42.2752	$42.28	$42.30	$42.30
Purchase #3	$140.84	10.284%	$155.324	$155.32	$155.30	$155.30
Purchase #4	$75.84	8.320%	$82.1499	$82.15	$82.15	$82.10
Purchase #5	$64.91	11.728%	$72.5226	$72.52	$72.50	$72.50
Purchase #6	$175.54	6.286%	$186.5744	$186.57	$186.55	$186.60
Purchase #7	$190.74	10.427%	$210.6285	$210.63	$210.65	$210.60
7 purchase totals =	$721.01		$784.6343	$784.63	$784.60	$784.60