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	$105.64	7.604%	$113.6729	$113.67	$113.65	$113.70
Purchase #2	$29.30	5.868%	$31.0193	$31.02	$31.00	$31.00
Purchase #3	$57.33	3.203%	$59.1663	$59.17	$59.15	$59.20
Purchase #4	$53.88	9.664%	$59.087	$59.09	$59.10	$59.10
Purchase #5	$6.78	8.165%	$7.3336	$7.33	$7.35	$7.30
Purchase #6	$233.48	9.241%	$255.0559	$255.06	$255.05	$255.10
Purchase #7	$15.34	5.413%	$16.1704	$16.17	$16.15	$16.20
7 purchase totals =	$501.75		$541.5054	$541.51	$541.45	$541.60