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	$185.39	3.419%	$191.7285	$191.73	$191.75	$191.70
Purchase #2	$227.45	8.789%	$247.4406	$247.44	$247.45	$247.40
Purchase #3	$150.62	6.810%	$160.8772	$160.88	$160.90	$160.90
Purchase #4	$147.66	11.497%	$164.6365	$164.64	$164.65	$164.60
Purchase #5	$73.95	11.504%	$82.4572	$82.46	$82.45	$82.50
Purchase #6	$88.32	4.144%	$91.98	$91.98	$92.00	$92.00
Purchase #7	$22.42	11.850%	$25.0768	$25.08	$25.10	$25.10
7 purchase totals =	$895.81		$964.1968	$964.21	$964.30	$964.20