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	$79.84	12.516%	$89.8328	$89.83	$89.85	$89.80
Purchase #2	$36.73	4.385%	$38.3406	$38.34	$38.35	$38.30
Purchase #3	$234.60	12.422%	$263.742	$263.74	$263.75	$263.70
Purchase #4	$241.47	13.654%	$274.4403	$274.44	$274.45	$274.40
Purchase #5	$243.86	13.198%	$276.0446	$276.04	$276.05	$276.00
Purchase #6	$231.51	5.118%	$243.3587	$243.36	$243.35	$243.40
Purchase #7	$235.54	3.424%	$243.6049	$243.60	$243.60	$243.60
7 purchase totals =	$1,303.55		$1,429.3639	$1,429.35	$1,429.40	$1,429.20