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	$29.73	6.221%	$31.5795	$31.58	$31.60	$31.60
Purchase #2	$42.76	7.445%	$45.9435	$45.94	$45.95	$45.90
Purchase #3	$160.89	11.416%	$179.2572	$179.26	$179.25	$179.30
Purchase #4	$180.80	9.228%	$197.4842	$197.48	$197.50	$197.50
Purchase #5	$149.59	3.239%	$154.4352	$154.44	$154.45	$154.40
Purchase #6	$88.90	3.396%	$91.919	$91.92	$91.90	$91.90
Purchase #7	$196.63	9.460%	$215.2312	$215.23	$215.25	$215.20
7 purchase totals =	$849.30		$915.8498	$915.85	$915.90	$915.80