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	$29.41	5.449%	$31.0126	$31.01	$31.00	$31.00
Purchase #2	$232.32	5.496%	$245.0883	$245.09	$245.10	$245.10
Purchase #3	$90.49	10.329%	$99.8367	$99.84	$99.85	$99.80
Purchase #4	$6.74	7.835%	$7.2681	$7.27	$7.25	$7.30
Purchase #5	$207.53	3.549%	$214.8952	$214.90	$214.90	$214.90
Purchase #6	$42.30	8.116%	$45.7331	$45.73	$45.75	$45.70
Purchase #7	$179.89	9.219%	$196.4741	$196.47	$196.45	$196.50
7 purchase totals =	$788.68		$840.3081	$840.31	$840.30	$840.30