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	$124.55	11.743%	$139.1759	$139.18	$139.20	$139.20
Purchase #2	$61.42	12.808%	$69.2867	$69.29	$69.30	$69.30
Purchase #3	$145.57	7.789%	$156.9084	$156.91	$156.90	$156.90
Purchase #4	$175.66	9.244%	$191.898	$191.90	$191.90	$191.90
Purchase #5	$99.52	7.102%	$106.5879	$106.59	$106.60	$106.60
Purchase #6	$156.62	9.555%	$171.585	$171.59	$171.60	$171.60
Purchase #7	$145.55	13.349%	$164.9795	$164.98	$165.00	$165.00
7 purchase totals =	$908.89		$1,000.4214	$1,000.44	$1,000.50	$1,000.50