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	$57.61	6.672%	$61.4537	$61.45	$61.45	$61.50
Purchase #2	$126.30	13.360%	$143.1737	$143.17	$143.15	$143.20
Purchase #3	$92.67	4.645%	$96.9745	$96.97	$96.95	$97.00
Purchase #4	$164.85	12.127%	$184.8414	$184.84	$184.85	$184.80
Purchase #5	$114.56	13.559%	$130.0932	$130.09	$130.10	$130.10
Purchase #6	$56.73	4.321%	$59.1813	$59.18	$59.20	$59.20
Purchase #7	$229.87	10.850%	$254.8109	$254.81	$254.80	$254.80
7 purchase totals =	$842.59		$930.5287	$930.51	$930.50	$930.60