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	$19.88	3.564%	$20.5885	$20.59	$20.60	$20.60
Purchase #2	$140.60	6.365%	$149.5492	$149.55	$149.55	$149.50
Purchase #3	$246.48	13.303%	$279.2692	$279.27	$279.25	$279.30
Purchase #4	$130.39	10.810%	$144.4852	$144.49	$144.50	$144.50
Purchase #5	$80.41	10.468%	$88.8273	$88.83	$88.85	$88.80
Purchase #6	$104.90	8.505%	$113.8217	$113.82	$113.80	$113.80
Purchase #7	$201.65	5.165%	$212.0652	$212.07	$212.05	$212.10
7 purchase totals =	$924.31		$1,008.6063	$1,008.62	$1,008.60	$1,008.60