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	$249.45	7.603%	$268.4157	$268.42	$268.40	$268.40
Purchase #2	$6.76	8.867%	$7.3594	$7.36	$7.35	$7.40
Purchase #3	$160.42	12.156%	$179.9207	$179.92	$179.90	$179.90
Purchase #4	$29.44	7.398%	$31.618	$31.62	$31.60	$31.60
Purchase #5	$182.74	9.668%	$200.4073	$200.41	$200.40	$200.40
Purchase #6	$172.99	5.524%	$182.546	$182.55	$182.55	$182.50
Purchase #7	$90.42	10.210%	$99.6519	$99.65	$99.65	$99.70
7 purchase totals =	$892.22		$969.9190	$969.93	$969.85	$969.90