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	$58.54	12.634%	$65.9359	$65.94	$65.95	$65.90
Purchase #2	$212.98	12.740%	$240.1137	$240.11	$240.10	$240.10
Purchase #3	$73.91	8.851%	$80.4518	$80.45	$80.45	$80.50
Purchase #4	$160.41	5.361%	$169.0096	$169.01	$169.00	$169.00
Purchase #5	$66.29	7.868%	$71.5057	$71.51	$71.50	$71.50
Purchase #6	$81.35	8.655%	$88.3908	$88.39	$88.40	$88.40
Purchase #7	$138.96	12.483%	$156.3064	$156.31	$156.30	$156.30
7 purchase totals =	$792.44		$871.7139	$871.72	$871.70	$871.70