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	$114.48	11.718%	$127.8948	$127.89	$127.90	$127.90
Purchase #2	$49.43	9.498%	$54.1249	$54.12	$54.10	$54.10
Purchase #3	$138.73	4.462%	$144.9201	$144.92	$144.90	$144.90
Purchase #4	$28.98	11.783%	$32.3947	$32.39	$32.40	$32.40
Purchase #5	$189.94	3.168%	$195.9573	$195.96	$195.95	$196.00
Purchase #6	$25.72	4.458%	$26.8666	$26.87	$26.85	$26.90
Purchase #7	$46.49	13.568%	$52.7978	$52.80	$52.80	$52.80
7 purchase totals =	$593.77		$634.9562	$634.95	$634.90	$635.00