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	$25.98	13.808%	$29.5673	$29.57	$29.55	$29.60
Purchase #2	$77.90	9.653%	$85.4197	$85.42	$85.40	$85.40
Purchase #3	$181.58	13.299%	$205.7283	$205.73	$205.75	$205.70
Purchase #4	$89.43	13.672%	$101.6569	$101.66	$101.65	$101.70
Purchase #5	$189.40	3.850%	$196.6919	$196.69	$196.70	$196.70
Purchase #6	$17.30	8.842%	$18.8297	$18.83	$18.85	$18.80
Purchase #7	$38.51	7.317%	$41.3278	$41.33	$41.35	$41.30
7 purchase totals =	$620.10		$679.2216	$679.23	$679.25	$679.20