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	$231.37	8.562%	$251.1799	$251.18	$251.20	$251.20
Purchase #2	$109.85	12.483%	$123.5626	$123.56	$123.55	$123.60
Purchase #3	$101.76	9.133%	$111.0537	$111.05	$111.05	$111.10
Purchase #4	$194.51	10.856%	$215.626	$215.63	$215.65	$215.60
Purchase #5	$159.93	11.848%	$178.8785	$178.88	$178.90	$178.90
Purchase #6	$200.54	13.674%	$227.9618	$227.96	$227.95	$228.00
Purchase #7	$215.55	12.645%	$242.8063	$242.81	$242.80	$242.80
7 purchase totals =	$1,213.51		$1,351.0688	$1,351.07	$1,351.10	$1,351.20