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	$70.62	13.303%	$80.0146	$80.01	$80.00	$80.00
Purchase #2	$180.76	6.356%	$192.2491	$192.25	$192.25	$192.20
Purchase #3	$234.91	5.817%	$248.5747	$248.57	$248.55	$248.60
Purchase #4	$156.61	12.200%	$175.7164	$175.72	$175.70	$175.70
Purchase #5	$33.38	10.347%	$36.8338	$36.83	$36.85	$36.80
Purchase #6	$148.47	13.729%	$168.8534	$168.85	$168.85	$168.90
Purchase #7	$78.79	4.370%	$82.2331	$82.23	$82.25	$82.20
7 purchase totals =	$903.54		$984.4751	$984.46	$984.45	$984.40