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	$17.78	13.797%	$20.2331	$20.23	$20.25	$20.20
Purchase #2	$226.83	9.154%	$247.594	$247.59	$247.60	$247.60
Purchase #3	$203.64	9.821%	$223.6395	$223.64	$223.65	$223.60
Purchase #4	$244.56	6.127%	$259.5442	$259.54	$259.55	$259.50
Purchase #5	$126.34	3.812%	$131.1561	$131.16	$131.15	$131.20
Purchase #6	$143.94	7.322%	$154.4793	$154.48	$154.50	$154.50
Purchase #7	$90.93	9.167%	$99.2656	$99.27	$99.25	$99.30
7 purchase totals =	$1,054.02		$1,135.9118	$1,135.91	$1,135.95	$1,135.90