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	$104.46	4.192%	$108.839	$108.84	$108.85	$108.80
Purchase #2	$117.34	7.472%	$126.1076	$126.11	$126.10	$126.10
Purchase #3	$74.31	11.516%	$82.8675	$82.87	$82.85	$82.90
Purchase #4	$128.35	5.614%	$135.5556	$135.56	$135.55	$135.60
Purchase #5	$17.54	10.378%	$19.3603	$19.36	$19.35	$19.40
Purchase #6	$147.78	3.218%	$152.5356	$152.54	$152.55	$152.50
Purchase #7	$13.44	3.131%	$13.8608	$13.86	$13.85	$13.90
7 purchase totals =	$603.22		$639.1264	$639.14	$639.10	$639.20