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	$104.76	6.812%	$111.8963	$111.90	$111.90	$111.90
Purchase #2	$95.57	6.294%	$101.5852	$101.59	$101.60	$101.60
Purchase #3	$215.28	3.528%	$222.8751	$222.88	$222.90	$222.90
Purchase #4	$108.31	7.383%	$116.3065	$116.31	$116.30	$116.30
Purchase #5	$152.98	12.511%	$172.1193	$172.12	$172.10	$172.10
Purchase #6	$116.41	6.806%	$124.3329	$124.33	$124.35	$124.30
Purchase #7	$97.77	3.663%	$101.3513	$101.35	$101.35	$101.40
7 purchase totals =	$891.08		$950.4666	$950.48	$950.50	$950.50