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	$242.31	13.456%	$274.9152	$274.92	$274.90	$274.90
Purchase #2	$20.88	6.185%	$22.1714	$22.17	$22.15	$22.20
Purchase #3	$78.64	3.523%	$81.4105	$81.41	$81.40	$81.40
Purchase #4	$229.64	6.441%	$244.4311	$244.43	$244.45	$244.40
Purchase #5	$150.59	3.727%	$156.2025	$156.20	$156.20	$156.20
Purchase #6	$53.34	11.145%	$59.2847	$59.28	$59.30	$59.30
Purchase #7	$103.51	9.586%	$113.4325	$113.43	$113.45	$113.40
7 purchase totals =	$878.91		$951.8479	$951.84	$951.85	$951.80