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	$188.78	10.468%	$208.5415	$208.54	$208.55	$208.50
Purchase #2	$56.49	3.235%	$58.3175	$58.32	$58.30	$58.30
Purchase #3	$97.29	9.588%	$106.6182	$106.62	$106.60	$106.60
Purchase #4	$166.85	13.532%	$189.4281	$189.43	$189.45	$189.40
Purchase #5	$122.28	12.141%	$137.126	$137.13	$137.15	$137.10
Purchase #6	$198.59	12.229%	$222.8756	$222.88	$222.90	$222.90
Purchase #7	$250.67	7.303%	$268.9764	$268.98	$269.00	$269.00
7 purchase totals =	$1,080.95		$1,191.8833	$1,191.90	$1,191.95	$1,191.80