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	$28.90	10.832%	$32.0304	$32.03	$32.05	$32.00
Purchase #2	$25.76	13.690%	$29.2865	$29.29	$29.30	$29.30
Purchase #3	$163.71	13.207%	$185.3312	$185.33	$185.35	$185.30
Purchase #4	$80.72	5.504%	$85.1628	$85.16	$85.15	$85.20
Purchase #5	$137.87	5.299%	$145.1757	$145.18	$145.20	$145.20
Purchase #6	$136.68	11.614%	$152.554	$152.55	$152.55	$152.60
Purchase #7	$31.88	5.713%	$33.7013	$33.70	$33.70	$33.70
7 purchase totals =	$605.52		$663.2419	$663.24	$663.30	$663.30