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	$55.55	10.670%	$61.4772	$61.48	$61.50	$61.50
Purchase #2	$131.66	8.371%	$142.6813	$142.68	$142.70	$142.70
Purchase #3	$235.76	12.144%	$264.3907	$264.39	$264.40	$264.40
Purchase #4	$176.26	3.555%	$182.526	$182.53	$182.55	$182.50
Purchase #5	$135.63	4.545%	$141.7944	$141.79	$141.80	$141.80
Purchase #6	$49.63	3.796%	$51.514	$51.51	$51.50	$51.50
Purchase #7	$115.85	10.111%	$127.5636	$127.56	$127.55	$127.60
7 purchase totals =	$900.34		$971.9472	$971.94	$972.00	$972.00