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	$73.82	12.874%	$83.3236	$83.32	$83.30	$83.30
Purchase #2	$94.63	9.267%	$103.3994	$103.40	$103.40	$103.40
Purchase #3	$74.83	5.532%	$78.9696	$78.97	$78.95	$79.00
Purchase #4	$217.69	4.843%	$228.2327	$228.23	$228.25	$228.20
Purchase #5	$210.63	3.696%	$218.4149	$218.41	$218.40	$218.40
Purchase #6	$88.51	13.813%	$100.7359	$100.74	$100.75	$100.70
Purchase #7	$78.79	13.443%	$89.3817	$89.38	$89.40	$89.40
7 purchase totals =	$838.90		$902.4578	$902.45	$902.45	$902.40