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	$155.36	10.790%	$172.1233	$172.12	$172.10	$172.10
Purchase #2	$39.33	5.702%	$41.5726	$41.57	$41.55	$41.60
Purchase #3	$101.32	10.560%	$112.0194	$112.02	$112.00	$112.00
Purchase #4	$143.53	9.230%	$156.7778	$156.78	$156.80	$156.80
Purchase #5	$96.52	9.679%	$105.8622	$105.86	$105.85	$105.90
Purchase #6	$25.90	13.443%	$29.3817	$29.38	$29.40	$29.40
Purchase #7	$29.34	9.596%	$32.1555	$32.16	$32.15	$32.20
7 purchase totals =	$591.30		$649.8925	$649.89	$649.85	$650.00