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	$212.46	5.394%	$223.9201	$223.92	$223.90	$223.90
Purchase #2	$31.73	6.755%	$33.8734	$33.87	$33.85	$33.90
Purchase #3	$74.48	7.857%	$80.3319	$80.33	$80.35	$80.30
Purchase #4	$109.69	10.194%	$120.8718	$120.87	$120.85	$120.90
Purchase #5	$38.61	3.486%	$39.9559	$39.96	$39.95	$40.00
Purchase #6	$59.97	8.305%	$64.9505	$64.95	$64.95	$65.00
Purchase #7	$24.29	13.508%	$27.5711	$27.57	$27.55	$27.60
7 purchase totals =	$551.23		$591.4747	$591.47	$591.40	$591.60