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	$99.78	12.148%	$111.9013	$111.90	$111.90	$111.90
Purchase #2	$116.69	9.165%	$127.3846	$127.38	$127.40	$127.40
Purchase #3	$163.84	9.832%	$179.9487	$179.95	$179.95	$179.90
Purchase #4	$13.87	5.459%	$14.6272	$14.63	$14.65	$14.60
Purchase #5	$93.31	13.244%	$105.668	$105.67	$105.65	$105.70
Purchase #6	$126.47	6.221%	$134.3377	$134.34	$134.35	$134.30
Purchase #7	$170.89	5.406%	$180.1283	$180.13	$180.15	$180.10
7 purchase totals =	$784.85		$853.9958	$854.00	$854.05	$853.90