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	$226.39	10.542%	$250.256	$250.26	$250.25	$250.30
Purchase #2	$9.28	10.377%	$10.243	$10.24	$10.25	$10.20
Purchase #3	$110.83	5.425%	$116.8425	$116.84	$116.85	$116.80
Purchase #4	$249.88	12.209%	$280.3878	$280.39	$280.40	$280.40
Purchase #5	$72.31	10.551%	$79.9394	$79.94	$79.95	$79.90
Purchase #6	$29.35	6.836%	$31.3564	$31.36	$31.35	$31.40
Purchase #7	$241.65	12.498%	$271.8514	$271.85	$271.85	$271.90
7 purchase totals =	$939.69		$1,040.8765	$1,040.88	$1,040.90	$1,040.90