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	$128.68	8.715%	$139.8945	$139.89	$139.90	$139.90
Purchase #2	$165.51	8.711%	$179.9276	$179.93	$179.95	$179.90
Purchase #3	$105.91	8.724%	$115.1496	$115.15	$115.15	$115.10
Purchase #4	$96.76	9.672%	$106.1186	$106.12	$106.10	$106.10
Purchase #5	$103.67	5.595%	$109.4703	$109.47	$109.45	$109.50
Purchase #6	$189.73	10.821%	$210.2607	$210.26	$210.25	$210.30
Purchase #7	$144.44	4.869%	$151.4728	$151.47	$151.45	$151.50
7 purchase totals =	$934.70		$1,012.2941	$1,012.29	$1,012.25	$1,012.30