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	$125.53	4.256%	$130.8726	$130.87	$130.85	$130.90
Purchase #2	$243.72	11.749%	$272.3547	$272.35	$272.35	$272.40
Purchase #3	$20.73	8.218%	$22.4336	$22.43	$22.45	$22.40
Purchase #4	$84.34	5.505%	$88.9829	$88.98	$89.00	$89.00
Purchase #5	$250.45	11.609%	$279.5247	$279.52	$279.50	$279.50
Purchase #6	$36.90	11.731%	$41.2287	$41.23	$41.25	$41.20
Purchase #7	$222.40	8.134%	$240.49	$240.49	$240.50	$240.50
7 purchase totals =	$984.07		$1,075.8872	$1,075.87	$1,075.90	$1,075.90