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	$24.93	12.786%	$28.1175	$28.12	$28.10	$28.10
Purchase #2	$133.59	8.267%	$144.6339	$144.63	$144.65	$144.60
Purchase #3	$247.46	8.222%	$267.8062	$267.81	$267.80	$267.80
Purchase #4	$202.80	6.451%	$215.8826	$215.88	$215.90	$215.90
Purchase #5	$132.35	11.640%	$147.7555	$147.76	$147.75	$147.80
Purchase #6	$196.50	8.335%	$212.8783	$212.88	$212.90	$212.90
Purchase #7	$169.61	5.684%	$179.2506	$179.25	$179.25	$179.30
7 purchase totals =	$1,107.24		$1,196.3246	$1,196.33	$1,196.35	$1,196.40