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	$42.47	6.611%	$45.2777	$45.28	$45.30	$45.30
Purchase #2	$80.89	10.383%	$89.2888	$89.29	$89.30	$89.30
Purchase #3	$86.83	6.533%	$92.5026	$92.50	$92.50	$92.50
Purchase #4	$176.59	4.368%	$184.3035	$184.30	$184.30	$184.30
Purchase #5	$143.26	6.260%	$152.2281	$152.23	$152.25	$152.20
Purchase #6	$10.80	10.628%	$11.9478	$11.95	$11.95	$11.90
Purchase #7	$225.80	3.727%	$234.2156	$234.22	$234.20	$234.20
7 purchase totals =	$766.64		$809.7641	$809.77	$809.80	$809.70