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	$18.26	7.308%	$19.5944	$19.59	$19.60	$19.60
Purchase #2	$23.89	12.558%	$26.8901	$26.89	$26.90	$26.90
Purchase #3	$82.33	9.290%	$89.9785	$89.98	$90.00	$90.00
Purchase #4	$97.74	11.773%	$109.2469	$109.25	$109.25	$109.20
Purchase #5	$66.92	6.439%	$71.229	$71.23	$71.25	$71.20
Purchase #6	$194.33	3.193%	$200.535	$200.54	$200.55	$200.50
Purchase #7	$107.89	6.274%	$114.659	$114.66	$114.65	$114.70
7 purchase totals =	$591.36		$632.1329	$632.14	$632.20	$632.10