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	$126.57	10.230%	$139.5181	$139.52	$139.50	$139.50
Purchase #2	$170.35	9.371%	$186.3135	$186.31	$186.30	$186.30
Purchase #3	$203.29	7.586%	$218.7116	$218.71	$218.70	$218.70
Purchase #4	$155.85	8.375%	$168.9024	$168.90	$168.90	$168.90
Purchase #5	$118.70	10.512%	$131.1777	$131.18	$131.20	$131.20
Purchase #6	$36.73	10.213%	$40.4812	$40.48	$40.50	$40.50
Purchase #7	$200.81	3.386%	$207.6094	$207.61	$207.60	$207.60
7 purchase totals =	$1,012.30		$1,092.7139	$1,092.71	$1,092.70	$1,092.70