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	$90.64	12.409%	$101.8875	$101.89	$101.90	$101.90
Purchase #2	$190.30	5.196%	$200.188	$200.19	$200.20	$200.20
Purchase #3	$25.28	8.176%	$27.3469	$27.35	$27.35	$27.30
Purchase #4	$76.83	7.718%	$82.7597	$82.76	$82.75	$82.80
Purchase #5	$125.52	3.152%	$129.4764	$129.48	$129.50	$129.50
Purchase #6	$43.64	4.578%	$45.6378	$45.64	$45.65	$45.60
Purchase #7	$198.90	7.565%	$213.9468	$213.95	$213.95	$213.90
7 purchase totals =	$751.11		$801.2431	$801.26	$801.30	$801.20