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	$80.54	10.450%	$88.9564	$88.96	$88.95	$89.00
Purchase #2	$236.78	3.498%	$245.0626	$245.06	$245.05	$245.10
Purchase #3	$100.71	11.566%	$112.3581	$112.36	$112.35	$112.40
Purchase #4	$116.67	13.762%	$132.7261	$132.73	$132.75	$132.70
Purchase #5	$7.28	10.602%	$8.0518	$8.05	$8.05	$8.10
Purchase #6	$53.42	10.515%	$59.0371	$59.04	$59.05	$59.00
Purchase #7	$178.27	12.588%	$200.7106	$200.71	$200.70	$200.70
7 purchase totals =	$773.67		$846.9027	$846.91	$846.90	$847.00