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	$140.33	12.718%	$158.1772	$158.18	$158.20	$158.20
Purchase #2	$71.63	9.654%	$78.5452	$78.55	$78.55	$78.50
Purchase #3	$65.45	11.568%	$73.0213	$73.02	$73.00	$73.00
Purchase #4	$105.69	7.633%	$113.7573	$113.76	$113.75	$113.80
Purchase #5	$28.58	9.364%	$31.2562	$31.26	$31.25	$31.30
Purchase #6	$156.79	5.410%	$165.2723	$165.27	$165.25	$165.30
Purchase #7	$192.75	6.571%	$205.4156	$205.42	$205.40	$205.40
7 purchase totals =	$761.22		$825.4451	$825.46	$825.40	$825.50