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	$26.89	6.586%	$28.661	$28.66	$28.65	$28.70
Purchase #2	$73.54	6.630%	$78.4157	$78.42	$78.40	$78.40
Purchase #3	$213.36	11.543%	$237.9881	$237.99	$238.00	$238.00
Purchase #4	$234.56	6.724%	$250.3318	$250.33	$250.35	$250.30
Purchase #5	$52.64	13.663%	$59.8322	$59.83	$59.85	$59.80
Purchase #6	$144.87	5.227%	$152.4424	$152.44	$152.45	$152.40
Purchase #7	$169.72	12.143%	$190.3291	$190.33	$190.35	$190.30
7 purchase totals =	$915.58		$998.0003	$998.00	$998.05	$997.90