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	$233.89	3.616%	$242.3475	$242.35	$242.35	$242.30
Purchase #2	$86.79	10.863%	$96.218	$96.22	$96.20	$96.20
Purchase #3	$33.83	11.593%	$37.7519	$37.75	$37.75	$37.80
Purchase #4	$100.55	3.159%	$103.7264	$103.73	$103.75	$103.70
Purchase #5	$158.52	11.282%	$176.4042	$176.40	$176.40	$176.40
Purchase #6	$89.34	12.829%	$100.8014	$100.80	$100.80	$100.80
Purchase #7	$157.95	11.134%	$175.5362	$175.54	$175.55	$175.50
7 purchase totals =	$860.87		$932.7856	$932.79	$932.80	$932.70