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	$250.40	10.154%	$275.8256	$275.83	$275.85	$275.80
Purchase #2	$100.57	11.191%	$111.8248	$111.82	$111.80	$111.80
Purchase #3	$193.40	9.745%	$212.2468	$212.25	$212.25	$212.20
Purchase #4	$70.65	6.799%	$75.4535	$75.45	$75.45	$75.50
Purchase #5	$29.75	5.484%	$31.3815	$31.38	$31.40	$31.40
Purchase #6	$99.66	3.287%	$102.9358	$102.94	$102.95	$102.90
Purchase #7	$79.54	9.603%	$87.1782	$87.18	$87.20	$87.20
7 purchase totals =	$823.97		$896.8462	$896.85	$896.90	$896.80