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	$116.32	10.143%	$128.1183	$128.12	$128.10	$128.10
Purchase #2	$17.71	4.336%	$18.4779	$18.48	$18.50	$18.50
Purchase #3	$213.38	7.523%	$229.4326	$229.43	$229.45	$229.40
Purchase #4	$91.46	5.400%	$96.3988	$96.40	$96.40	$96.40
Purchase #5	$202.40	8.282%	$219.1628	$219.16	$219.15	$219.20
Purchase #6	$86.80	4.462%	$90.673	$90.67	$90.65	$90.70
Purchase #7	$69.97	11.360%	$77.9186	$77.92	$77.90	$77.90
7 purchase totals =	$798.04		$860.1820	$860.18	$860.15	$860.20