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	$96.34	11.627%	$107.5415	$107.54	$107.55	$107.50
Purchase #2	$108.32	6.730%	$115.6099	$115.61	$115.60	$115.60
Purchase #3	$34.89	13.468%	$39.589	$39.59	$39.60	$39.60
Purchase #4	$229.95	10.788%	$254.757	$254.76	$254.75	$254.80
Purchase #5	$180.29	8.822%	$196.1952	$196.20	$196.20	$196.20
Purchase #6	$91.72	5.576%	$96.8343	$96.83	$96.85	$96.80
Purchase #7	$135.66	11.209%	$150.8661	$150.87	$150.85	$150.90
7 purchase totals =	$877.17		$961.3930	$961.40	$961.40	$961.40