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	$40.62	11.791%	$45.4095	$45.41	$45.40	$45.40
Purchase #2	$200.34	10.231%	$220.8368	$220.84	$220.85	$220.80
Purchase #3	$28.96	9.793%	$31.7961	$31.80	$31.80	$31.80
Purchase #4	$137.45	3.342%	$142.0436	$142.04	$142.05	$142.00
Purchase #5	$55.41	10.277%	$61.1045	$61.10	$61.10	$61.10
Purchase #6	$75.91	7.361%	$81.4977	$81.50	$81.50	$81.50
Purchase #7	$65.66	8.856%	$71.4748	$71.47	$71.45	$71.50
7 purchase totals =	$604.35		$654.1630	$654.16	$654.15	$654.10