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	$95.42	5.401%	$100.5736	$100.57	$100.55	$100.60
Purchase #2	$135.38	10.170%	$149.1481	$149.15	$149.15	$149.10
Purchase #3	$99.34	3.199%	$102.5179	$102.52	$102.50	$102.50
Purchase #4	$152.25	6.660%	$162.3899	$162.39	$162.40	$162.40
Purchase #5	$93.86	4.440%	$98.0274	$98.03	$98.05	$98.00
Purchase #6	$161.33	6.686%	$172.1165	$172.12	$172.10	$172.10
Purchase #7	$158.65	12.867%	$179.0635	$179.06	$179.05	$179.10
7 purchase totals =	$896.23		$963.8369	$963.84	$963.80	$963.80