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	$242.61	13.740%	$275.9446	$275.94	$275.95	$275.90
Purchase #2	$228.67	4.562%	$239.1019	$239.10	$239.10	$239.10
Purchase #3	$99.27	4.587%	$103.8235	$103.82	$103.80	$103.80
Purchase #4	$169.94	10.276%	$187.403	$187.40	$187.40	$187.40
Purchase #5	$113.55	3.539%	$117.5685	$117.57	$117.55	$117.60
Purchase #6	$52.85	12.599%	$59.5086	$59.51	$59.50	$59.50
Purchase #7	$178.33	5.229%	$187.6549	$187.65	$187.65	$187.70
7 purchase totals =	$1,085.22		$1,171.0050	$1,170.99	$1,170.95	$1,171.00