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	$146.33	9.638%	$160.4333	$160.43	$160.45	$160.40
Purchase #2	$62.50	5.800%	$66.125	$66.13	$66.15	$66.10
Purchase #3	$211.80	13.673%	$240.7594	$240.76	$240.75	$240.80
Purchase #4	$111.54	9.309%	$121.9233	$121.92	$121.90	$121.90
Purchase #5	$61.56	6.861%	$65.7836	$65.78	$65.80	$65.80
Purchase #6	$197.33	11.571%	$220.1631	$220.16	$220.15	$220.20
Purchase #7	$194.39	8.661%	$211.2261	$211.23	$211.25	$211.20
7 purchase totals =	$985.45		$1,086.4138	$1,086.41	$1,086.45	$1,086.40