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	$38.77	10.427%	$42.8125	$42.81	$42.80	$42.80
Purchase #2	$231.59	8.268%	$250.7379	$250.74	$250.75	$250.70
Purchase #3	$16.61	13.134%	$18.7916	$18.79	$18.80	$18.80
Purchase #4	$31.96	3.806%	$33.1764	$33.18	$33.20	$33.20
Purchase #5	$102.54	9.121%	$111.8927	$111.89	$111.90	$111.90
Purchase #6	$200.43	6.405%	$213.2675	$213.27	$213.25	$213.30
Purchase #7	$187.77	7.778%	$202.3748	$202.37	$202.35	$202.40
7 purchase totals =	$809.67		$873.0534	$873.05	$873.05	$873.10