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	$91.84	11.651%	$102.5403	$102.54	$102.55	$102.50
Purchase #2	$137.37	5.128%	$144.4143	$144.41	$144.40	$144.40
Purchase #3	$198.58	3.328%	$205.1887	$205.19	$205.20	$205.20
Purchase #4	$240.39	10.482%	$265.5877	$265.59	$265.60	$265.60
Purchase #5	$38.79	12.164%	$43.5084	$43.51	$43.50	$43.50
Purchase #6	$89.99	7.556%	$96.7896	$96.79	$96.80	$96.80
Purchase #7	$223.49	12.169%	$250.6865	$250.69	$250.70	$250.70
7 purchase totals =	$1,020.45		$1,108.7155	$1,108.72	$1,108.75	$1,108.70