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	$71.50	10.300%	$78.8645	$78.86	$78.85	$78.90
Purchase #2	$192.80	6.444%	$205.224	$205.22	$205.20	$205.20
Purchase #3	$7.33	5.402%	$7.726	$7.73	$7.75	$7.70
Purchase #4	$236.95	5.789%	$250.667	$250.67	$250.65	$250.70
Purchase #5	$36.90	3.220%	$38.0882	$38.09	$38.10	$38.10
Purchase #6	$159.79	13.640%	$181.5854	$181.59	$181.60	$181.60
Purchase #7	$48.39	11.865%	$54.1315	$54.13	$54.15	$54.10
7 purchase totals =	$753.66		$816.2866	$816.29	$816.30	$816.30