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	$22.91	10.371%	$25.286	$25.29	$25.30	$25.30
Purchase #2	$135.28	8.586%	$146.8951	$146.90	$146.90	$146.90
Purchase #3	$153.87	11.705%	$171.8805	$171.88	$171.90	$171.90
Purchase #4	$178.59	5.323%	$188.0963	$188.10	$188.10	$188.10
Purchase #5	$90.83	3.580%	$94.0817	$94.08	$94.10	$94.10
Purchase #6	$137.78	3.656%	$142.8172	$142.82	$142.80	$142.80
Purchase #7	$210.83	6.227%	$223.9584	$223.96	$223.95	$224.00
7 purchase totals =	$930.09		$993.0152	$993.03	$993.05	$993.10