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	$128.62	8.326%	$139.3289	$139.33	$139.35	$139.30
Purchase #2	$220.72	13.485%	$250.4841	$250.48	$250.50	$250.50
Purchase #3	$52.86	11.397%	$58.8845	$58.88	$58.90	$58.90
Purchase #4	$59.61	13.173%	$67.4624	$67.46	$67.45	$67.50
Purchase #5	$118.44	6.574%	$126.2262	$126.23	$126.25	$126.20
Purchase #6	$158.55	5.246%	$166.8675	$166.87	$166.85	$166.90
Purchase #7	$69.79	4.258%	$72.7617	$72.76	$72.75	$72.80
7 purchase totals =	$808.59		$882.0153	$882.01	$882.05	$882.10