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	$170.86	5.558%	$180.3564	$180.36	$180.35	$180.40
Purchase #2	$185.82	5.813%	$196.6217	$196.62	$196.60	$196.60
Purchase #3	$223.53	13.334%	$253.3355	$253.34	$253.35	$253.30
Purchase #4	$30.40	10.374%	$33.5537	$33.55	$33.55	$33.60
Purchase #5	$50.89	13.573%	$57.7973	$57.80	$57.80	$57.80
Purchase #6	$175.86	10.295%	$193.9648	$193.96	$193.95	$194.00
Purchase #7	$173.75	11.798%	$194.249	$194.25	$194.25	$194.20
7 purchase totals =	$1,011.11		$1,109.8784	$1,109.88	$1,109.85	$1,109.90