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	$86.79	5.718%	$91.7527	$91.75	$91.75	$91.80
Purchase #2	$136.37	4.641%	$142.6989	$142.70	$142.70	$142.70
Purchase #3	$231.83	13.336%	$262.7468	$262.75	$262.75	$262.70
Purchase #4	$113.59	5.728%	$120.0964	$120.10	$120.10	$120.10
Purchase #5	$113.34	12.435%	$127.4338	$127.43	$127.45	$127.40
Purchase #6	$102.26	6.686%	$109.0971	$109.10	$109.10	$109.10
Purchase #7	$46.78	10.859%	$51.8598	$51.86	$51.85	$51.90
7 purchase totals =	$830.96		$905.6855	$905.69	$905.70	$905.70