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	$232.51	10.566%	$257.077	$257.08	$257.10	$257.10
Purchase #2	$208.53	3.374%	$215.5658	$215.57	$215.55	$215.60
Purchase #3	$24.52	13.313%	$27.7843	$27.78	$27.80	$27.80
Purchase #4	$189.84	12.619%	$213.7959	$213.80	$213.80	$213.80
Purchase #5	$78.73	13.736%	$89.5444	$89.54	$89.55	$89.50
Purchase #6	$32.33	10.382%	$35.6865	$35.69	$35.70	$35.70
Purchase #7	$34.50	11.332%	$38.4095	$38.41	$38.40	$38.40
7 purchase totals =	$800.96		$877.8634	$877.87	$877.90	$877.90