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	$34.89	10.275%	$38.4749	$38.47	$38.45	$38.50
Purchase #2	$99.81	12.133%	$111.9199	$111.92	$111.90	$111.90
Purchase #3	$155.64	12.734%	$175.4592	$175.46	$175.45	$175.50
Purchase #4	$198.71	5.756%	$210.1477	$210.15	$210.15	$210.10
Purchase #5	$210.69	6.402%	$224.1784	$224.18	$224.20	$224.20
Purchase #6	$167.84	8.250%	$181.6868	$181.69	$181.70	$181.70
Purchase #7	$185.92	12.525%	$209.2065	$209.21	$209.20	$209.20
7 purchase totals =	$1,053.50		$1,151.0734	$1,151.08	$1,151.05	$1,151.10