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	$241.62	12.122%	$270.9092	$270.91	$270.90	$270.90
Purchase #2	$60.64	6.822%	$64.7769	$64.78	$64.80	$64.80
Purchase #3	$39.94	6.537%	$42.5509	$42.55	$42.55	$42.60
Purchase #4	$55.54	10.442%	$61.3395	$61.34	$61.35	$61.30
Purchase #5	$13.33	4.802%	$13.9701	$13.97	$13.95	$14.00
Purchase #6	$71.57	12.833%	$80.7546	$80.75	$80.75	$80.80
Purchase #7	$88.38	12.538%	$99.4611	$99.46	$99.45	$99.50
7 purchase totals =	$571.02		$633.7623	$633.76	$633.75	$633.90