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	$40.80	3.141%	$42.0815	$42.08	$42.10	$42.10
Purchase #2	$140.56	12.410%	$158.0035	$158.00	$158.00	$158.00
Purchase #3	$133.77	5.220%	$140.7528	$140.75	$140.75	$140.80
Purchase #4	$165.58	3.448%	$171.2892	$171.29	$171.30	$171.30
Purchase #5	$158.54	13.310%	$179.6417	$179.64	$179.65	$179.60
Purchase #6	$79.76	5.127%	$83.8493	$83.85	$83.85	$83.80
Purchase #7	$32.85	12.108%	$36.8275	$36.83	$36.85	$36.80
7 purchase totals =	$751.86		$812.4455	$812.44	$812.50	$812.40