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	$62.59	13.791%	$71.2218	$71.22	$71.20	$71.20
Purchase #2	$34.52	10.188%	$38.0369	$38.04	$38.05	$38.00
Purchase #3	$94.72	4.582%	$99.0601	$99.06	$99.05	$99.10
Purchase #4	$134.47	3.373%	$139.0057	$139.01	$139.00	$139.00
Purchase #5	$30.67	7.753%	$33.0478	$33.05	$33.05	$33.00
Purchase #6	$97.82	4.641%	$102.3598	$102.36	$102.35	$102.40
Purchase #7	$134.73	13.444%	$152.8431	$152.84	$152.85	$152.80
7 purchase totals =	$589.52		$635.5752	$635.58	$635.55	$635.50