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	$36.41	5.619%	$38.4559	$38.46	$38.45	$38.50
Purchase #2	$175.98	11.400%	$196.0417	$196.04	$196.05	$196.00
Purchase #3	$79.42	6.282%	$84.4092	$84.41	$84.40	$84.40
Purchase #4	$229.93	13.124%	$260.106	$260.11	$260.10	$260.10
Purchase #5	$134.96	9.457%	$147.7232	$147.72	$147.70	$147.70
Purchase #6	$107.72	3.552%	$111.5462	$111.55	$111.55	$111.50
Purchase #7	$240.33	10.279%	$265.0335	$265.03	$265.05	$265.00
7 purchase totals =	$1,004.75		$1,103.3157	$1,103.32	$1,103.30	$1,103.20