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	$64.61	7.815%	$69.6593	$69.66	$69.65	$69.70
Purchase #2	$218.56	13.860%	$248.8524	$248.85	$248.85	$248.90
Purchase #3	$129.77	7.420%	$139.3989	$139.40	$139.40	$139.40
Purchase #4	$55.58	6.587%	$59.2411	$59.24	$59.25	$59.20
Purchase #5	$250.57	6.141%	$265.9575	$265.96	$265.95	$266.00
Purchase #6	$97.51	13.304%	$110.4827	$110.48	$110.50	$110.50
Purchase #7	$105.59	3.818%	$109.6214	$109.62	$109.60	$109.60
7 purchase totals =	$922.19		$1,003.2133	$1,003.21	$1,003.20	$1,003.30