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	$24.89	11.467%	$27.7441	$27.74	$27.75	$27.70
Purchase #2	$26.70	3.623%	$27.6673	$27.67	$27.65	$27.70
Purchase #3	$92.51	13.618%	$105.108	$105.11	$105.10	$105.10
Purchase #4	$45.70	9.445%	$50.0164	$50.02	$50.00	$50.00
Purchase #5	$180.44	11.284%	$200.8008	$200.80	$200.80	$200.80
Purchase #6	$18.95	13.333%	$21.4766	$21.48	$21.50	$21.50
Purchase #7	$114.32	3.247%	$118.032	$118.03	$118.05	$118.00
7 purchase totals =	$503.51		$550.8452	$550.85	$550.85	$550.80