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	$98.79	4.374%	$103.1111	$103.11	$103.10	$103.10
Purchase #2	$228.58	4.802%	$239.5564	$239.56	$239.55	$239.60
Purchase #3	$146.40	6.465%	$155.8648	$155.86	$155.85	$155.90
Purchase #4	$140.51	6.743%	$149.9846	$149.98	$150.00	$150.00
Purchase #5	$86.82	3.657%	$89.995	$90.00	$90.00	$90.00
Purchase #6	$168.36	13.856%	$191.688	$191.69	$191.70	$191.70
Purchase #7	$20.35	6.818%	$21.7375	$21.74	$21.75	$21.70
7 purchase totals =	$889.81		$951.9374	$951.94	$951.95	$952.00