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	$75.80	3.868%	$78.7319	$78.73	$78.75	$78.70
Purchase #2	$171.28	6.677%	$182.7164	$182.72	$182.70	$182.70
Purchase #3	$28.87	4.531%	$30.1781	$30.18	$30.20	$30.20
Purchase #4	$32.44	11.491%	$36.1677	$36.17	$36.15	$36.20
Purchase #5	$185.36	6.191%	$196.8356	$196.84	$196.85	$196.80
Purchase #6	$227.61	11.762%	$254.3815	$254.38	$254.40	$254.40
Purchase #7	$81.67	4.440%	$85.2961	$85.30	$85.30	$85.30
7 purchase totals =	$803.03		$864.3073	$864.32	$864.35	$864.30