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	$99.85	3.157%	$103.0023	$103.00	$103.00	$103.00
Purchase #2	$137.90	10.766%	$152.7463	$152.75	$152.75	$152.70
Purchase #3	$35.68	13.578%	$40.5246	$40.52	$40.50	$40.50
Purchase #4	$65.37	9.326%	$71.4664	$71.47	$71.45	$71.50
Purchase #5	$229.35	13.146%	$259.5004	$259.50	$259.50	$259.50
Purchase #6	$223.88	7.785%	$241.3091	$241.31	$241.30	$241.30
Purchase #7	$168.97	13.262%	$191.3788	$191.38	$191.40	$191.40
7 purchase totals =	$961.00		$1,059.9279	$1,059.93	$1,059.90	$1,059.90