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	$137.57	11.130%	$152.8815	$152.88	$152.90	$152.90
Purchase #2	$242.57	10.602%	$268.2873	$268.29	$268.30	$268.30
Purchase #3	$90.99	7.868%	$98.1491	$98.15	$98.15	$98.10
Purchase #4	$37.29	11.429%	$41.5519	$41.55	$41.55	$41.60
Purchase #5	$179.57	11.424%	$200.0841	$200.08	$200.10	$200.10
Purchase #6	$91.66	5.422%	$96.6298	$96.63	$96.65	$96.60
Purchase #7	$49.65	8.105%	$53.6741	$53.67	$53.65	$53.70
7 purchase totals =	$829.30		$911.2578	$911.25	$911.30	$911.30