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	$19.46	11.279%	$21.6549	$21.65	$21.65	$21.70
Purchase #2	$185.69	13.153%	$210.1138	$210.11	$210.10	$210.10
Purchase #3	$141.44	4.448%	$147.7313	$147.73	$147.75	$147.70
Purchase #4	$119.52	3.118%	$123.2466	$123.25	$123.25	$123.20
Purchase #5	$227.87	10.397%	$251.5616	$251.56	$251.55	$251.60
Purchase #6	$96.28	4.169%	$100.2939	$100.29	$100.30	$100.30
Purchase #7	$126.97	9.653%	$139.2264	$139.23	$139.25	$139.20
7 purchase totals =	$917.23		$993.8285	$993.82	$993.85	$993.80