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	$37.65	11.644%	$42.034	$42.03	$42.05	$42.00
Purchase #2	$123.25	7.737%	$132.7859	$132.79	$132.80	$132.80
Purchase #3	$156.43	3.811%	$162.3915	$162.39	$162.40	$162.40
Purchase #4	$246.76	13.568%	$280.2404	$280.24	$280.25	$280.20
Purchase #5	$146.76	9.409%	$160.5686	$160.57	$160.55	$160.60
Purchase #6	$208.32	11.817%	$232.9372	$232.94	$232.95	$232.90
Purchase #7	$173.40	9.260%	$189.4568	$189.46	$189.45	$189.50
7 purchase totals =	$1,092.57		$1,200.4144	$1,200.42	$1,200.45	$1,200.40