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	$25.95	4.608%	$27.1458	$27.15	$27.15	$27.10
Purchase #2	$147.52	7.199%	$158.14	$158.14	$158.15	$158.10
Purchase #3	$103.90	3.532%	$107.5697	$107.57	$107.55	$107.60
Purchase #4	$115.69	3.445%	$119.6755	$119.68	$119.70	$119.70
Purchase #5	$181.85	5.310%	$191.5062	$191.51	$191.50	$191.50
Purchase #6	$123.48	12.818%	$139.3077	$139.31	$139.30	$139.30
Purchase #7	$240.36	11.723%	$268.5374	$268.54	$268.55	$268.50
7 purchase totals =	$938.75		$1,011.8823	$1,011.90	$1,011.90	$1,011.80