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	$156.40	8.502%	$169.6971	$169.70	$169.70	$169.70
Purchase #2	$30.64	12.781%	$34.5561	$34.56	$34.55	$34.60
Purchase #3	$27.86	10.829%	$30.877	$30.88	$30.90	$30.90
Purchase #4	$103.64	5.475%	$109.3143	$109.31	$109.30	$109.30
Purchase #5	$192.73	6.619%	$205.4868	$205.49	$205.50	$205.50
Purchase #6	$36.62	3.372%	$37.8548	$37.85	$37.85	$37.90
Purchase #7	$218.61	9.122%	$238.5516	$238.55	$238.55	$238.60
7 purchase totals =	$766.50		$826.3377	$826.34	$826.35	$826.50