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	$77.76	3.521%	$80.4979	$80.50	$80.50	$80.50
Purchase #2	$240.55	8.659%	$261.3792	$261.38	$261.40	$261.40
Purchase #3	$151.59	10.549%	$167.5812	$167.58	$167.60	$167.60
Purchase #4	$237.25	4.326%	$247.5134	$247.51	$247.50	$247.50
Purchase #5	$60.43	13.116%	$68.356	$68.36	$68.35	$68.40
Purchase #6	$123.79	6.521%	$131.8623	$131.86	$131.85	$131.90
Purchase #7	$75.84	3.753%	$78.6863	$78.69	$78.70	$78.70
7 purchase totals =	$967.21		$1,035.8763	$1,035.88	$1,035.90	$1,036.00