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	$11.64	4.261%	$12.136	$12.14	$12.15	$12.10
Purchase #2	$197.40	7.336%	$211.8813	$211.88	$211.90	$211.90
Purchase #3	$213.58	8.435%	$231.5955	$231.60	$231.60	$231.60
Purchase #4	$82.74	7.801%	$89.1945	$89.19	$89.20	$89.20
Purchase #5	$150.84	11.329%	$167.9287	$167.93	$167.95	$167.90
Purchase #6	$59.76	11.136%	$66.4149	$66.41	$66.40	$66.40
Purchase #7	$153.73	4.322%	$160.3742	$160.37	$160.35	$160.40
7 purchase totals =	$869.69		$939.5251	$939.52	$939.55	$939.50