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	$51.81	6.105%	$54.973	$54.97	$54.95	$55.00
Purchase #2	$132.33	10.870%	$146.7143	$146.71	$146.70	$146.70
Purchase #3	$16.83	8.493%	$18.2594	$18.26	$18.25	$18.30
Purchase #4	$242.71	8.478%	$263.287	$263.29	$263.30	$263.30
Purchase #5	$67.34	8.229%	$72.8814	$72.88	$72.90	$72.90
Purchase #6	$35.61	9.726%	$39.0734	$39.07	$39.05	$39.10
Purchase #7	$131.44	6.623%	$140.1453	$140.15	$140.15	$140.10
7 purchase totals =	$678.07		$735.3338	$735.33	$735.30	$735.40