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	$77.34	3.630%	$80.1474	$80.15	$80.15	$80.10
Purchase #2	$67.30	7.582%	$72.4027	$72.40	$72.40	$72.40
Purchase #3	$58.70	3.234%	$60.5984	$60.60	$60.60	$60.60
Purchase #4	$231.36	7.671%	$249.1076	$249.11	$249.10	$249.10
Purchase #5	$38.89	6.742%	$41.512	$41.51	$41.50	$41.50
Purchase #6	$192.41	8.335%	$208.4474	$208.45	$208.45	$208.40
Purchase #7	$135.42	11.819%	$151.4253	$151.43	$151.45	$151.40
7 purchase totals =	$801.42		$863.6408	$863.65	$863.65	$863.50