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	$71.41	11.190%	$79.4008	$79.40	$79.40	$79.40
Purchase #2	$186.96	7.259%	$200.5314	$200.53	$200.55	$200.50
Purchase #3	$17.92	9.294%	$19.5855	$19.59	$19.60	$19.60
Purchase #4	$172.85	5.802%	$182.8788	$182.88	$182.90	$182.90
Purchase #5	$181.44	7.175%	$194.4583	$194.46	$194.45	$194.50
Purchase #6	$227.77	12.292%	$255.7675	$255.77	$255.75	$255.80
Purchase #7	$37.38	10.793%	$41.4144	$41.41	$41.40	$41.40
7 purchase totals =	$895.73		$974.0367	$974.04	$974.05	$974.10