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	$109.31	8.148%	$118.2166	$118.22	$118.20	$118.20
Purchase #2	$44.31	9.163%	$48.3701	$48.37	$48.35	$48.40
Purchase #3	$207.92	10.828%	$230.4336	$230.43	$230.45	$230.40
Purchase #4	$97.84	7.655%	$105.3297	$105.33	$105.35	$105.30
Purchase #5	$114.88	7.346%	$123.3191	$123.32	$123.30	$123.30
Purchase #6	$84.69	5.692%	$89.5106	$89.51	$89.50	$89.50
Purchase #7	$220.58	9.136%	$240.7322	$240.73	$240.75	$240.70
7 purchase totals =	$879.53		$955.9119	$955.91	$955.90	$955.80