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	$46.73	11.110%	$51.9217	$51.92	$51.90	$51.90
Purchase #2	$151.90	5.529%	$160.2986	$160.30	$160.30	$160.30
Purchase #3	$184.57	6.649%	$196.8421	$196.84	$196.85	$196.80
Purchase #4	$160.73	11.387%	$179.0323	$179.03	$179.05	$179.00
Purchase #5	$177.32	6.279%	$188.4539	$188.45	$188.45	$188.50
Purchase #6	$88.35	5.149%	$92.8991	$92.90	$92.90	$92.90
Purchase #7	$46.85	5.519%	$49.4357	$49.44	$49.45	$49.40
7 purchase totals =	$856.45		$918.8834	$918.88	$918.90	$918.80