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	$207.56	5.116%	$218.1788	$218.18	$218.20	$218.20
Purchase #2	$183.53	11.710%	$205.0214	$205.02	$205.00	$205.00
Purchase #3	$135.94	3.340%	$140.4804	$140.48	$140.50	$140.50
Purchase #4	$78.61	8.843%	$85.5615	$85.56	$85.55	$85.60
Purchase #5	$109.73	13.387%	$124.4196	$124.42	$124.40	$124.40
Purchase #6	$200.94	7.379%	$215.7674	$215.77	$215.75	$215.80
Purchase #7	$66.99	8.132%	$72.4376	$72.44	$72.45	$72.40
7 purchase totals =	$983.30		$1,061.8667	$1,061.87	$1,061.85	$1,061.90