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	$94.32	3.809%	$97.9126	$97.91	$97.90	$97.90
Purchase #2	$165.85	12.739%	$186.9776	$186.98	$187.00	$187.00
Purchase #3	$93.51	6.637%	$99.7163	$99.72	$99.70	$99.70
Purchase #4	$109.70	6.583%	$116.9216	$116.92	$116.90	$116.90
Purchase #5	$93.28	8.768%	$101.4588	$101.46	$101.45	$101.50
Purchase #6	$146.54	4.116%	$152.5716	$152.57	$152.55	$152.60
Purchase #7	$153.44	8.183%	$165.996	$166.00	$166.00	$166.00
7 purchase totals =	$856.64		$921.5545	$921.56	$921.50	$921.60