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	$33.70	7.690%	$36.2915	$36.29	$36.30	$36.30
Purchase #2	$223.56	11.384%	$249.0101	$249.01	$249.00	$249.00
Purchase #3	$163.42	11.162%	$181.6609	$181.66	$181.65	$181.70
Purchase #4	$83.53	10.815%	$92.5638	$92.56	$92.55	$92.60
Purchase #5	$145.42	3.673%	$150.7613	$150.76	$150.75	$150.80
Purchase #6	$124.53	12.391%	$139.9605	$139.96	$139.95	$140.00
Purchase #7	$168.40	12.275%	$189.0711	$189.07	$189.05	$189.10
7 purchase totals =	$942.56		$1,039.3192	$1,039.31	$1,039.25	$1,039.50