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	$9.53	4.376%	$9.947	$9.95	$9.95	$9.90
Purchase #2	$18.57	12.501%	$20.8914	$20.89	$20.90	$20.90
Purchase #3	$201.93	3.837%	$209.6781	$209.68	$209.70	$209.70
Purchase #4	$140.69	10.539%	$155.5173	$155.52	$155.50	$155.50
Purchase #5	$96.30	7.854%	$103.8634	$103.86	$103.85	$103.90
Purchase #6	$52.73	5.859%	$55.8195	$55.82	$55.80	$55.80
Purchase #7	$82.97	13.673%	$94.3145	$94.31	$94.30	$94.30
7 purchase totals =	$602.72		$650.0312	$650.03	$650.00	$650.00