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	$115.57	6.631%	$123.2334	$123.23	$123.25	$123.20
Purchase #2	$39.77	6.157%	$42.2186	$42.22	$42.20	$42.20
Purchase #3	$42.81	9.351%	$46.8132	$46.81	$46.80	$46.80
Purchase #4	$36.90	7.172%	$39.5465	$39.55	$39.55	$39.50
Purchase #5	$242.87	8.771%	$264.1721	$264.17	$264.15	$264.20
Purchase #6	$6.51	5.288%	$6.8542	$6.85	$6.85	$6.90
Purchase #7	$31.68	6.772%	$33.8254	$33.83	$33.85	$33.80
7 purchase totals =	$516.11		$556.6634	$556.66	$556.65	$556.60