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	$240.56	10.293%	$265.3208	$265.32	$265.30	$265.30
Purchase #2	$103.89	11.485%	$115.8218	$115.82	$115.80	$115.80
Purchase #3	$18.95	13.219%	$21.455	$21.46	$21.45	$21.50
Purchase #4	$80.26	3.158%	$82.7946	$82.79	$82.80	$82.80
Purchase #5	$191.33	13.840%	$217.8101	$217.81	$217.80	$217.80
Purchase #6	$192.42	7.505%	$206.8611	$206.86	$206.85	$206.90
Purchase #7	$170.90	12.873%	$192.9	$192.90	$192.90	$192.90
7 purchase totals =	$998.31		$1,102.9634	$1,102.96	$1,102.90	$1,103.00