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	$39.58	5.809%	$41.8792	$41.88	$41.90	$41.90
Purchase #2	$6.93	9.459%	$7.5855	$7.59	$7.60	$7.60
Purchase #3	$58.87	3.766%	$61.087	$61.09	$61.10	$61.10
Purchase #4	$123.74	5.267%	$130.2574	$130.26	$130.25	$130.30
Purchase #5	$84.37	3.632%	$87.4343	$87.43	$87.45	$87.40
Purchase #6	$86.88	3.285%	$89.734	$89.73	$89.75	$89.70
Purchase #7	$241.83	9.267%	$264.2404	$264.24	$264.25	$264.20
7 purchase totals =	$642.20		$682.2178	$682.22	$682.30	$682.20