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	$36.98	5.141%	$38.8811	$38.88	$38.90	$38.90
Purchase #2	$59.30	3.277%	$61.2433	$61.24	$61.25	$61.20
Purchase #3	$106.98	9.736%	$117.3956	$117.40	$117.40	$117.40
Purchase #4	$164.34	10.688%	$181.9047	$181.90	$181.90	$181.90
Purchase #5	$37.69	10.714%	$41.7281	$41.73	$41.75	$41.70
Purchase #6	$170.99	11.459%	$190.5837	$190.58	$190.60	$190.60
Purchase #7	$65.80	8.132%	$71.1509	$71.15	$71.15	$71.20
7 purchase totals =	$642.08		$702.8874	$702.88	$702.95	$702.90