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	$38.84	4.275%	$40.5004	$40.50	$40.50	$40.50
Purchase #2	$212.59	3.675%	$220.4027	$220.40	$220.40	$220.40
Purchase #3	$162.30	12.479%	$182.5534	$182.55	$182.55	$182.60
Purchase #4	$48.90	11.861%	$54.7	$54.70	$54.70	$54.70
Purchase #5	$238.71	10.157%	$262.9558	$262.96	$262.95	$263.00
Purchase #6	$54.73	7.835%	$59.0181	$59.02	$59.00	$59.00
Purchase #7	$224.27	5.389%	$236.3559	$236.36	$236.35	$236.40
7 purchase totals =	$980.34		$1,056.4863	$1,056.49	$1,056.45	$1,056.60