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	$70.89	3.645%	$73.4739	$73.47	$73.45	$73.50
Purchase #2	$91.70	9.228%	$100.1621	$100.16	$100.15	$100.20
Purchase #3	$38.73	9.771%	$42.5143	$42.51	$42.50	$42.50
Purchase #4	$236.73	5.675%	$250.1644	$250.16	$250.15	$250.20
Purchase #5	$156.53	10.366%	$172.7559	$172.76	$172.75	$172.80
Purchase #6	$176.46	5.793%	$186.6823	$186.68	$186.70	$186.70
Purchase #7	$240.56	5.438%	$253.6417	$253.64	$253.65	$253.60
7 purchase totals =	$1,011.60		$1,079.3946	$1,079.38	$1,079.35	$1,079.50