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	$34.34	11.459%	$38.275	$38.28	$38.30	$38.30
Purchase #2	$78.79	12.741%	$88.8286	$88.83	$88.85	$88.80
Purchase #3	$25.43	7.802%	$27.414	$27.41	$27.40	$27.40
Purchase #4	$130.79	9.218%	$142.8462	$142.85	$142.85	$142.80
Purchase #5	$111.50	4.470%	$116.4841	$116.48	$116.50	$116.50
Purchase #6	$203.69	3.196%	$210.1999	$210.20	$210.20	$210.20
Purchase #7	$223.83	5.143%	$235.3416	$235.34	$235.35	$235.30
7 purchase totals =	$808.37		$859.3894	$859.39	$859.45	$859.30