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	$79.35	4.700%	$83.0795	$83.08	$83.10	$83.10
Purchase #2	$42.72	3.717%	$44.3079	$44.31	$44.30	$44.30
Purchase #3	$96.31	10.517%	$106.4389	$106.44	$106.45	$106.40
Purchase #4	$173.56	13.354%	$196.7372	$196.74	$196.75	$196.70
Purchase #5	$39.42	10.438%	$43.5347	$43.53	$43.55	$43.50
Purchase #6	$93.52	4.492%	$97.7209	$97.72	$97.70	$97.70
Purchase #7	$52.99	7.306%	$56.8614	$56.86	$56.85	$56.90
7 purchase totals =	$577.87		$628.6805	$628.68	$628.70	$628.60