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	$161.41	6.116%	$171.2818	$171.28	$171.30	$171.30
Purchase #2	$73.32	12.512%	$82.4938	$82.49	$82.50	$82.50
Purchase #3	$238.85	10.760%	$264.5503	$264.55	$264.55	$264.60
Purchase #4	$87.62	7.181%	$93.912	$93.91	$93.90	$93.90
Purchase #5	$32.49	7.349%	$34.8777	$34.88	$34.90	$34.90
Purchase #6	$73.58	10.781%	$81.5127	$81.51	$81.50	$81.50
Purchase #7	$93.66	4.798%	$98.1538	$98.15	$98.15	$98.20
7 purchase totals =	$760.93		$826.7821	$826.77	$826.80	$826.90