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	$47.80	5.695%	$50.5222	$50.52	$50.50	$50.50
Purchase #2	$33.98	7.391%	$36.4915	$36.49	$36.50	$36.50
Purchase #3	$76.61	4.292%	$79.8981	$79.90	$79.90	$79.90
Purchase #4	$157.47	6.143%	$167.1434	$167.14	$167.15	$167.10
Purchase #5	$82.94	8.566%	$90.0446	$90.04	$90.05	$90.00
Purchase #6	$221.98	3.212%	$229.11	$229.11	$229.10	$229.10
Purchase #7	$38.39	4.611%	$40.1602	$40.16	$40.15	$40.20
7 purchase totals =	$659.17		$693.3700	$693.36	$693.35	$693.30