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	$146.78	9.372%	$160.5362	$160.54	$160.55	$160.50
Purchase #2	$228.50	12.459%	$256.9688	$256.97	$256.95	$257.00
Purchase #3	$71.71	4.543%	$74.9678	$74.97	$74.95	$75.00
Purchase #4	$29.84	5.797%	$31.5698	$31.57	$31.55	$31.60
Purchase #5	$237.32	9.114%	$258.9493	$258.95	$258.95	$258.90
Purchase #6	$59.30	9.425%	$64.889	$64.89	$64.90	$64.90
Purchase #7	$57.41	4.383%	$59.9263	$59.93	$59.95	$59.90
7 purchase totals =	$830.86		$907.8072	$907.82	$907.80	$907.80