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	$239.74	6.168%	$254.5272	$254.53	$254.55	$254.50
Purchase #2	$222.45	5.694%	$235.1163	$235.12	$235.10	$235.10
Purchase #3	$128.87	6.488%	$137.2311	$137.23	$137.25	$137.20
Purchase #4	$116.85	12.632%	$131.6105	$131.61	$131.60	$131.60
Purchase #5	$171.39	7.722%	$184.6247	$184.62	$184.60	$184.60
Purchase #6	$72.55	4.638%	$75.9149	$75.91	$75.90	$75.90
Purchase #7	$189.81	13.558%	$215.5444	$215.54	$215.55	$215.50
7 purchase totals =	$1,141.66		$1,234.5691	$1,234.56	$1,234.55	$1,234.40