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	$27.31	12.480%	$30.7183	$30.72	$30.70	$30.70
Purchase #2	$224.97	12.661%	$253.4535	$253.45	$253.45	$253.50
Purchase #3	$178.76	12.326%	$200.794	$200.79	$200.80	$200.80
Purchase #4	$165.87	12.402%	$186.4412	$186.44	$186.45	$186.40
Purchase #5	$49.39	12.516%	$55.5717	$55.57	$55.55	$55.60
Purchase #6	$229.37	13.360%	$260.0138	$260.01	$260.00	$260.00
Purchase #7	$176.86	4.778%	$185.3104	$185.31	$185.30	$185.30
7 purchase totals =	$1,052.53		$1,172.3029	$1,172.29	$1,172.25	$1,172.30