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	$79.49	11.377%	$88.5336	$88.53	$88.55	$88.50
Purchase #2	$230.42	5.248%	$242.5124	$242.51	$242.50	$242.50
Purchase #3	$87.85	13.549%	$99.7528	$99.75	$99.75	$99.80
Purchase #4	$104.49	3.474%	$108.12	$108.12	$108.10	$108.10
Purchase #5	$144.75	4.340%	$151.0322	$151.03	$151.05	$151.00
Purchase #6	$79.82	12.629%	$89.9005	$89.90	$89.90	$89.90
Purchase #7	$71.46	9.167%	$78.0107	$78.01	$78.00	$78.00
7 purchase totals =	$798.28		$857.8622	$857.85	$857.85	$857.80