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	$30.35	4.172%	$31.6162	$31.62	$31.60	$31.60
Purchase #2	$53.84	10.541%	$59.5153	$59.52	$59.50	$59.50
Purchase #3	$66.36	10.543%	$73.3563	$73.36	$73.35	$73.40
Purchase #4	$16.83	7.317%	$18.0615	$18.06	$18.05	$18.10
Purchase #5	$91.79	13.614%	$104.2863	$104.29	$104.30	$104.30
Purchase #6	$29.59	12.702%	$33.3485	$33.35	$33.35	$33.30
Purchase #7	$146.95	13.360%	$166.5825	$166.58	$166.60	$166.60
7 purchase totals =	$435.71		$486.7666	$486.78	$486.75	$486.80