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	$103.47	3.330%	$106.9156	$106.92	$106.90	$106.90
Purchase #2	$41.58	4.553%	$43.4731	$43.47	$43.45	$43.50
Purchase #3	$100.46	8.728%	$109.2281	$109.23	$109.25	$109.20
Purchase #4	$34.52	6.362%	$36.7162	$36.72	$36.70	$36.70
Purchase #5	$84.91	6.625%	$90.5353	$90.54	$90.55	$90.50
Purchase #6	$150.82	11.640%	$168.3754	$168.38	$168.40	$168.40
Purchase #7	$201.89	11.505%	$225.1174	$225.12	$225.10	$225.10
7 purchase totals =	$717.65		$780.3611	$780.38	$780.35	$780.30