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	$96.27	7.873%	$103.8493	$103.85	$103.85	$103.80
Purchase #2	$180.45	6.135%	$191.5206	$191.52	$191.50	$191.50
Purchase #3	$78.94	13.789%	$89.825	$89.83	$89.85	$89.80
Purchase #4	$15.96	8.459%	$17.3101	$17.31	$17.30	$17.30
Purchase #5	$26.36	4.438%	$27.5299	$27.53	$27.55	$27.50
Purchase #6	$28.25	9.132%	$30.8298	$30.83	$30.85	$30.80
Purchase #7	$125.86	4.556%	$131.5942	$131.59	$131.60	$131.60
7 purchase totals =	$552.09		$592.4589	$592.46	$592.50	$592.30