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	$234.86	3.413%	$242.8758	$242.88	$242.90	$242.90
Purchase #2	$149.38	11.261%	$166.2017	$166.20	$166.20	$166.20
Purchase #3	$88.50	4.540%	$92.5179	$92.52	$92.50	$92.50
Purchase #4	$5.58	10.801%	$6.1827	$6.18	$6.20	$6.20
Purchase #5	$235.93	12.192%	$264.6946	$264.69	$264.70	$264.70
Purchase #6	$180.38	11.351%	$200.8549	$200.85	$200.85	$200.90
Purchase #7	$127.54	8.605%	$138.5148	$138.51	$138.50	$138.50
7 purchase totals =	$1,022.17		$1,111.8424	$1,111.83	$1,111.85	$1,111.90