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	$239.46	10.543%	$264.7063	$264.71	$264.70	$264.70
Purchase #2	$174.36	11.719%	$194.7932	$194.79	$194.80	$194.80
Purchase #3	$237.59	7.456%	$255.3047	$255.30	$255.30	$255.30
Purchase #4	$176.35	11.645%	$196.886	$196.89	$196.90	$196.90
Purchase #5	$184.53	10.440%	$203.7949	$203.79	$203.80	$203.80
Purchase #6	$180.46	5.289%	$190.0045	$190.00	$190.00	$190.00
Purchase #7	$60.75	10.768%	$67.2916	$67.29	$67.30	$67.30
7 purchase totals =	$1,253.50		$1,372.7812	$1,372.77	$1,372.80	$1,372.80