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	$55.27	6.791%	$59.0234	$59.02	$59.00	$59.00
Purchase #2	$166.55	13.826%	$189.5772	$189.58	$189.60	$189.60
Purchase #3	$35.83	12.493%	$40.3062	$40.31	$40.30	$40.30
Purchase #4	$117.71	9.132%	$128.4593	$128.46	$128.45	$128.50
Purchase #5	$229.59	4.721%	$240.4289	$240.43	$240.45	$240.40
Purchase #6	$181.48	12.134%	$203.5008	$203.50	$203.50	$203.50
Purchase #7	$167.57	5.563%	$176.8919	$176.89	$176.90	$176.90
7 purchase totals =	$954.00		$1,038.1877	$1,038.19	$1,038.20	$1,038.20