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	$219.67	9.171%	$239.8159	$239.82	$239.80	$239.80
Purchase #2	$106.77	5.292%	$112.4203	$112.42	$112.40	$112.40
Purchase #3	$229.33	8.286%	$248.3323	$248.33	$248.35	$248.30
Purchase #4	$78.45	13.799%	$89.2753	$89.28	$89.30	$89.30
Purchase #5	$175.50	3.645%	$181.897	$181.90	$181.90	$181.90
Purchase #6	$10.41	3.662%	$10.7912	$10.79	$10.80	$10.80
Purchase #7	$183.71	3.640%	$190.397	$190.40	$190.40	$190.40
7 purchase totals =	$1,003.84		$1,072.9290	$1,072.94	$1,072.95	$1,072.90