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	$28.40	4.178%	$29.5866	$29.59	$29.60	$29.60
Purchase #2	$120.27	11.843%	$134.5136	$134.51	$134.50	$134.50
Purchase #3	$199.46	11.435%	$222.2683	$222.27	$222.25	$222.30
Purchase #4	$39.80	13.465%	$45.1591	$45.16	$45.15	$45.20
Purchase #5	$116.51	4.731%	$122.0221	$122.02	$122.00	$122.00
Purchase #6	$65.66	8.512%	$71.249	$71.25	$71.25	$71.20
Purchase #7	$56.89	7.626%	$61.2284	$61.23	$61.25	$61.20
7 purchase totals =	$626.99		$686.0271	$686.03	$686.00	$686.00