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	$83.89	6.360%	$89.2254	$89.23	$89.25	$89.20
Purchase #2	$98.94	3.310%	$102.2149	$102.21	$102.20	$102.20
Purchase #3	$186.63	3.379%	$192.9362	$192.94	$192.95	$192.90
Purchase #4	$141.74	4.666%	$148.3536	$148.35	$148.35	$148.40
Purchase #5	$107.77	8.193%	$116.5996	$116.60	$116.60	$116.60
Purchase #6	$36.39	8.155%	$39.3576	$39.36	$39.35	$39.40
Purchase #7	$69.88	11.481%	$77.9029	$77.90	$77.90	$77.90
7 purchase totals =	$725.24		$766.5902	$766.59	$766.60	$766.60