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	$20.32	7.665%	$21.8775	$21.88	$21.90	$21.90
Purchase #2	$134.57	10.373%	$148.5289	$148.53	$148.55	$148.50
Purchase #3	$196.39	11.681%	$219.3303	$219.33	$219.35	$219.30
Purchase #4	$55.54	7.393%	$59.6461	$59.65	$59.65	$59.60
Purchase #5	$90.37	11.829%	$101.0599	$101.06	$101.05	$101.10
Purchase #6	$128.32	11.140%	$142.6148	$142.61	$142.60	$142.60
Purchase #7	$246.94	12.375%	$277.4988	$277.50	$277.50	$277.50
7 purchase totals =	$872.45		$970.5563	$970.56	$970.60	$970.50