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	$250.69	11.853%	$280.4043	$280.40	$280.40	$280.40
Purchase #2	$209.73	13.105%	$237.2151	$237.22	$237.20	$237.20
Purchase #3	$37.36	12.363%	$41.9788	$41.98	$42.00	$42.00
Purchase #4	$183.74	3.642%	$190.4318	$190.43	$190.45	$190.40
Purchase #5	$173.51	8.503%	$188.2636	$188.26	$188.25	$188.30
Purchase #6	$200.63	4.835%	$210.3305	$210.33	$210.35	$210.30
Purchase #7	$50.60	3.247%	$52.243	$52.24	$52.25	$52.20
7 purchase totals =	$1,106.26		$1,200.8671	$1,200.86	$1,200.90	$1,200.80