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	$5.49	7.384%	$5.8954	$5.90	$5.90	$5.90
Purchase #2	$211.48	6.536%	$225.3023	$225.30	$225.30	$225.30
Purchase #3	$156.25	9.143%	$170.5359	$170.54	$170.55	$170.50
Purchase #4	$82.49	9.275%	$90.1409	$90.14	$90.15	$90.10
Purchase #5	$242.28	8.689%	$263.3317	$263.33	$263.35	$263.30
Purchase #6	$157.32	10.675%	$174.1139	$174.11	$174.10	$174.10
Purchase #7	$204.79	7.855%	$220.8763	$220.88	$220.90	$220.90
7 purchase totals =	$1,060.10		$1,150.1964	$1,150.20	$1,150.25	$1,150.10