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	$128.44	8.728%	$139.6502	$139.65	$139.65	$139.70
Purchase #2	$120.29	8.866%	$130.9549	$130.95	$130.95	$131.00
Purchase #3	$240.45	4.157%	$250.4455	$250.45	$250.45	$250.40
Purchase #4	$59.43	12.149%	$66.6502	$66.65	$66.65	$66.70
Purchase #5	$223.40	11.261%	$248.5571	$248.56	$248.55	$248.60
Purchase #6	$215.57	3.389%	$222.8757	$222.88	$222.90	$222.90
Purchase #7	$245.76	10.345%	$271.1839	$271.18	$271.20	$271.20
7 purchase totals =	$1,233.34		$1,330.3175	$1,330.32	$1,330.35	$1,330.50