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	$125.98	11.306%	$140.2233	$140.22	$140.20	$140.20
Purchase #2	$123.44	3.810%	$128.1431	$128.14	$128.15	$128.10
Purchase #3	$211.61	13.694%	$240.5879	$240.59	$240.60	$240.60
Purchase #4	$154.39	13.378%	$175.0443	$175.04	$175.05	$175.00
Purchase #5	$219.83	10.215%	$242.2856	$242.29	$242.30	$242.30
Purchase #6	$199.83	7.480%	$214.7773	$214.78	$214.80	$214.80
Purchase #7	$73.81	11.866%	$82.5683	$82.57	$82.55	$82.60
7 purchase totals =	$1,108.89		$1,223.6298	$1,223.63	$1,223.65	$1,223.60