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	$54.59	7.815%	$58.8562	$58.86	$58.85	$58.90
Purchase #2	$129.68	8.301%	$140.4447	$140.44	$140.45	$140.40
Purchase #3	$41.64	11.270%	$46.3328	$46.33	$46.35	$46.30
Purchase #4	$56.53	3.320%	$58.4068	$58.41	$58.40	$58.40
Purchase #5	$21.49	5.169%	$22.6008	$22.60	$22.60	$22.60
Purchase #6	$99.69	4.230%	$103.9069	$103.91	$103.90	$103.90
Purchase #7	$65.96	10.300%	$72.7539	$72.75	$72.75	$72.80
7 purchase totals =	$469.58		$503.3021	$503.30	$503.30	$503.30