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	$41.98	3.562%	$43.4753	$43.48	$43.50	$43.50
Purchase #2	$52.33	5.470%	$55.1925	$55.19	$55.20	$55.20
Purchase #3	$210.87	11.553%	$235.2318	$235.23	$235.25	$235.20
Purchase #4	$38.41	10.763%	$42.5441	$42.54	$42.55	$42.50
Purchase #5	$25.54	12.526%	$28.7391	$28.74	$28.75	$28.70
Purchase #6	$33.38	5.228%	$35.1251	$35.13	$35.15	$35.10
Purchase #7	$132.49	9.460%	$145.0236	$145.02	$145.00	$145.00
7 purchase totals =	$535.00		$585.3315	$585.33	$585.40	$585.20