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	$80.81	12.112%	$90.5977	$90.60	$90.60	$90.60
Purchase #2	$160.40	9.834%	$176.1737	$176.17	$176.15	$176.20
Purchase #3	$69.82	12.368%	$78.4553	$78.46	$78.45	$78.50
Purchase #4	$175.77	6.138%	$186.5588	$186.56	$186.55	$186.60
Purchase #5	$58.37	6.828%	$62.3555	$62.36	$62.35	$62.40
Purchase #6	$201.57	9.282%	$220.2797	$220.28	$220.30	$220.30
Purchase #7	$103.26	7.802%	$111.3163	$111.32	$111.30	$111.30
7 purchase totals =	$850.00		$925.7370	$925.75	$925.70	$925.90