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	$25.69	7.696%	$27.6671	$27.67	$27.65	$27.70
Purchase #2	$92.26	8.229%	$99.8521	$99.85	$99.85	$99.90
Purchase #3	$185.86	12.568%	$209.2189	$209.22	$209.20	$209.20
Purchase #4	$206.98	3.262%	$213.7317	$213.73	$213.75	$213.70
Purchase #5	$50.73	10.151%	$55.8796	$55.88	$55.90	$55.90
Purchase #6	$237.89	4.714%	$249.1041	$249.10	$249.10	$249.10
Purchase #7	$247.86	4.532%	$259.093	$259.09	$259.10	$259.10
7 purchase totals =	$1,047.27		$1,114.5465	$1,114.54	$1,114.55	$1,114.60