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	$37.40	6.464%	$39.8175	$39.82	$39.80	$39.80
Purchase #2	$168.58	10.788%	$186.7664	$186.77	$186.75	$186.80
Purchase #3	$235.45	10.441%	$260.0333	$260.03	$260.05	$260.00
Purchase #4	$68.46	13.250%	$77.531	$77.53	$77.55	$77.50
Purchase #5	$62.85	7.300%	$67.4381	$67.44	$67.45	$67.40
Purchase #6	$199.65	11.649%	$222.9072	$222.91	$222.90	$222.90
Purchase #7	$229.74	11.339%	$255.7902	$255.79	$255.80	$255.80
7 purchase totals =	$1,002.13		$1,110.2837	$1,110.29	$1,110.30	$1,110.20