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	$158.83	13.728%	$180.6342	$180.63	$180.65	$180.60
Purchase #2	$61.97	9.807%	$68.0474	$68.05	$68.05	$68.00
Purchase #3	$80.94	10.442%	$89.3918	$89.39	$89.40	$89.40
Purchase #4	$135.33	6.316%	$143.8774	$143.88	$143.90	$143.90
Purchase #5	$168.47	13.731%	$191.6026	$191.60	$191.60	$191.60
Purchase #6	$42.49	12.791%	$47.9249	$47.92	$47.90	$47.90
Purchase #7	$123.63	5.529%	$130.4655	$130.47	$130.45	$130.50
7 purchase totals =	$771.66		$851.9438	$851.94	$851.95	$851.90