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	$241.33	6.234%	$256.3745	$256.37	$256.35	$256.40
Purchase #2	$31.50	13.580%	$35.7777	$35.78	$35.80	$35.80
Purchase #3	$170.54	6.435%	$181.5142	$181.51	$181.50	$181.50
Purchase #4	$165.30	12.696%	$186.2865	$186.29	$186.30	$186.30
Purchase #5	$73.88	10.868%	$81.9093	$81.91	$81.90	$81.90
Purchase #6	$68.48	3.338%	$70.7659	$70.77	$70.75	$70.80
Purchase #7	$235.31	12.699%	$265.192	$265.19	$265.20	$265.20
7 purchase totals =	$986.34		$1,077.8201	$1,077.82	$1,077.80	$1,077.90