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	$29.53	6.457%	$31.4368	$31.44	$31.45	$31.40
Purchase #2	$147.95	9.631%	$162.1991	$162.20	$162.20	$162.20
Purchase #3	$41.78	8.451%	$45.3108	$45.31	$45.30	$45.30
Purchase #4	$179.35	5.445%	$189.1156	$189.12	$189.10	$189.10
Purchase #5	$82.57	9.291%	$90.2416	$90.24	$90.25	$90.20
Purchase #6	$123.62	6.551%	$131.7183	$131.72	$131.70	$131.70
Purchase #7	$117.45	5.249%	$123.615	$123.62	$123.60	$123.60
7 purchase totals =	$722.25		$773.6372	$773.65	$773.60	$773.50