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	$44.90	5.501%	$47.3699	$47.37	$47.35	$47.40
Purchase #2	$201.64	11.756%	$225.3448	$225.34	$225.35	$225.30
Purchase #3	$187.72	4.164%	$195.5367	$195.54	$195.55	$195.50
Purchase #4	$37.70	4.183%	$39.277	$39.28	$39.30	$39.30
Purchase #5	$100.53	9.301%	$109.8803	$109.88	$109.90	$109.90
Purchase #6	$9.77	3.799%	$10.1412	$10.14	$10.15	$10.10
Purchase #7	$39.51	3.740%	$40.9877	$40.99	$41.00	$41.00
7 purchase totals =	$621.77		$668.5376	$668.54	$668.60	$668.50