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	$38.60	10.385%	$42.6086	$42.61	$42.60	$42.60
Purchase #2	$242.56	10.156%	$267.1944	$267.19	$267.20	$267.20
Purchase #3	$109.50	13.847%	$124.6625	$124.66	$124.65	$124.70
Purchase #4	$76.85	10.548%	$84.9561	$84.96	$84.95	$85.00
Purchase #5	$220.50	12.546%	$248.1639	$248.16	$248.15	$248.20
Purchase #6	$53.96	10.622%	$59.6916	$59.69	$59.70	$59.70
Purchase #7	$81.42	12.219%	$91.3687	$91.37	$91.35	$91.40
7 purchase totals =	$823.39		$918.6458	$918.64	$918.60	$918.80