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	$52.47	8.827%	$57.1015	$57.10	$57.10	$57.10
Purchase #2	$134.44	7.661%	$144.7394	$144.74	$144.75	$144.70
Purchase #3	$222.66	6.740%	$237.6673	$237.67	$237.65	$237.70
Purchase #4	$72.42	12.597%	$81.5427	$81.54	$81.55	$81.50
Purchase #5	$41.72	8.782%	$45.3839	$45.38	$45.40	$45.40
Purchase #6	$80.49	10.710%	$89.1105	$89.11	$89.10	$89.10
Purchase #7	$230.83	6.272%	$245.3077	$245.31	$245.30	$245.30
7 purchase totals =	$835.03		$900.8530	$900.85	$900.85	$900.80