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	$127.54	13.596%	$144.8803	$144.88	$144.90	$144.90
Purchase #2	$93.71	13.303%	$106.1762	$106.18	$106.20	$106.20
Purchase #3	$24.83	13.364%	$28.1483	$28.15	$28.15	$28.10
Purchase #4	$247.39	6.752%	$264.0938	$264.09	$264.10	$264.10
Purchase #5	$74.33	12.184%	$83.3864	$83.39	$83.40	$83.40
Purchase #6	$158.39	12.802%	$178.6671	$178.67	$178.65	$178.70
Purchase #7	$36.50	8.560%	$39.6244	$39.62	$39.60	$39.60
7 purchase totals =	$762.69		$844.9765	$844.98	$845.00	$845.00