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	$115.77	4.118%	$120.5374	$120.54	$120.55	$120.50
Purchase #2	$228.92	13.380%	$259.5495	$259.55	$259.55	$259.50
Purchase #3	$134.66	8.829%	$146.5491	$146.55	$146.55	$146.50
Purchase #4	$102.66	3.556%	$106.3106	$106.31	$106.30	$106.30
Purchase #5	$6.31	13.182%	$7.1418	$7.14	$7.15	$7.10
Purchase #6	$98.83	12.332%	$111.0177	$111.02	$111.00	$111.00
Purchase #7	$247.64	11.439%	$275.9675	$275.97	$275.95	$276.00
7 purchase totals =	$934.79		$1,027.0736	$1,027.08	$1,027.05	$1,026.90