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	$79.90	12.727%	$90.0689	$90.07	$90.05	$90.10
Purchase #2	$122.49	9.128%	$133.6709	$133.67	$133.65	$133.70
Purchase #3	$71.33	3.127%	$73.5605	$73.56	$73.55	$73.60
Purchase #4	$116.38	3.561%	$120.5243	$120.52	$120.50	$120.50
Purchase #5	$27.91	13.785%	$31.7574	$31.76	$31.75	$31.80
Purchase #6	$125.84	9.548%	$137.8552	$137.86	$137.85	$137.90
Purchase #7	$240.48	7.522%	$258.5689	$258.57	$258.55	$258.60
7 purchase totals =	$784.33		$846.0061	$846.01	$845.90	$846.20