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	$158.84	6.767%	$169.5887	$169.59	$169.60	$169.60
Purchase #2	$189.64	5.596%	$200.2523	$200.25	$200.25	$200.30
Purchase #3	$233.93	12.553%	$263.2952	$263.30	$263.30	$263.30
Purchase #4	$169.76	6.330%	$180.5058	$180.51	$180.50	$180.50
Purchase #5	$89.73	11.111%	$99.6999	$99.70	$99.70	$99.70
Purchase #6	$74.97	12.683%	$84.4784	$84.48	$84.50	$84.50
Purchase #7	$123.59	12.839%	$139.4577	$139.46	$139.45	$139.50
7 purchase totals =	$1,040.46		$1,137.2780	$1,137.29	$1,137.30	$1,137.40