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	$51.25	7.498%	$55.0927	$55.09	$55.10	$55.10
Purchase #2	$154.30	9.281%	$168.6206	$168.62	$168.60	$168.60
Purchase #3	$15.33	3.201%	$15.8207	$15.82	$15.80	$15.80
Purchase #4	$41.33	12.452%	$46.4764	$46.48	$46.50	$46.50
Purchase #5	$157.70	10.300%	$173.9431	$173.94	$173.95	$173.90
Purchase #6	$25.67	10.324%	$28.3202	$28.32	$28.30	$28.30
Purchase #7	$18.71	12.368%	$21.0241	$21.02	$21.00	$21.00
7 purchase totals =	$464.29		$509.2978	$509.29	$509.25	$509.20