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	$247.70	10.614%	$273.9909	$273.99	$274.00	$274.00
Purchase #2	$190.51	5.121%	$200.266	$200.27	$200.25	$200.30
Purchase #3	$76.54	3.554%	$79.2602	$79.26	$79.25	$79.30
Purchase #4	$67.56	4.276%	$70.4489	$70.45	$70.45	$70.40
Purchase #5	$218.94	12.263%	$245.7886	$245.79	$245.80	$245.80
Purchase #6	$163.83	13.671%	$186.2272	$186.23	$186.25	$186.20
Purchase #7	$130.74	10.495%	$144.4612	$144.46	$144.45	$144.50
7 purchase totals =	$1,095.82		$1,200.4430	$1,200.45	$1,200.45	$1,200.50