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	$244.96	10.168%	$269.8675	$269.87	$269.85	$269.90
Purchase #2	$204.69	8.559%	$222.2094	$222.21	$222.20	$222.20
Purchase #3	$169.82	12.765%	$191.4975	$191.50	$191.50	$191.50
Purchase #4	$210.94	5.856%	$223.2926	$223.29	$223.30	$223.30
Purchase #5	$178.41	12.532%	$200.7683	$200.77	$200.75	$200.80
Purchase #6	$55.84	12.174%	$62.638	$62.64	$62.65	$62.60
Purchase #7	$82.34	6.360%	$87.5768	$87.58	$87.60	$87.60
7 purchase totals =	$1,147.00		$1,257.8501	$1,257.86	$1,257.85	$1,257.90