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	$112.36	6.761%	$119.9567	$119.96	$119.95	$120.00
Purchase #2	$87.56	3.219%	$90.3786	$90.38	$90.40	$90.40
Purchase #3	$188.93	4.320%	$197.0918	$197.09	$197.10	$197.10
Purchase #4	$205.45	12.512%	$231.1559	$231.16	$231.15	$231.20
Purchase #5	$83.46	7.357%	$89.6002	$89.60	$89.60	$89.60
Purchase #6	$237.40	11.431%	$264.5372	$264.54	$264.55	$264.50
Purchase #7	$95.96	13.582%	$108.9933	$108.99	$109.00	$109.00
7 purchase totals =	$1,011.12		$1,101.7137	$1,101.72	$1,101.75	$1,101.80