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	$149.94	9.792%	$164.6221	$164.62	$164.60	$164.60
Purchase #2	$249.80	6.454%	$265.9221	$265.92	$265.90	$265.90
Purchase #3	$197.45	7.445%	$212.1502	$212.15	$212.15	$212.20
Purchase #4	$165.59	8.221%	$179.2032	$179.20	$179.20	$179.20
Purchase #5	$237.62	4.528%	$248.3794	$248.38	$248.40	$248.40
Purchase #6	$79.55	12.635%	$89.6011	$89.60	$89.60	$89.60
Purchase #7	$222.48	4.241%	$231.9154	$231.92	$231.90	$231.90
7 purchase totals =	$1,302.43		$1,391.7935	$1,391.79	$1,391.75	$1,391.80