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	$94.28	3.815%	$97.8768	$97.88	$97.90	$97.90
Purchase #2	$109.57	12.731%	$123.5194	$123.52	$123.50	$123.50
Purchase #3	$222.63	3.210%	$229.7764	$229.78	$229.80	$229.80
Purchase #4	$166.66	10.303%	$183.831	$183.83	$183.85	$183.80
Purchase #5	$86.57	12.666%	$97.535	$97.54	$97.55	$97.50
Purchase #6	$154.36	12.597%	$173.8047	$173.80	$173.80	$173.80
Purchase #7	$28.31	13.776%	$32.21	$32.21	$32.20	$32.20
7 purchase totals =	$862.38		$938.5533	$938.56	$938.60	$938.50