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	$232.77	13.234%	$263.5748	$263.57	$263.55	$263.60
Purchase #2	$128.73	10.559%	$142.3226	$142.32	$142.30	$142.30
Purchase #3	$230.83	13.350%	$261.6458	$261.65	$261.65	$261.60
Purchase #4	$46.47	11.240%	$51.6932	$51.69	$51.70	$51.70
Purchase #5	$98.57	4.577%	$103.0815	$103.08	$103.10	$103.10
Purchase #6	$61.92	4.789%	$64.8853	$64.89	$64.90	$64.90
Purchase #7	$96.25	4.743%	$100.8151	$100.82	$100.80	$100.80
7 purchase totals =	$895.54		$988.0183	$988.02	$988.00	$988.00