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	$233.56	9.278%	$255.2297	$255.23	$255.25	$255.20
Purchase #2	$187.29	10.183%	$206.3617	$206.36	$206.35	$206.40
Purchase #3	$210.94	5.771%	$223.1133	$223.11	$223.10	$223.10
Purchase #4	$22.71	7.716%	$24.4623	$24.46	$24.45	$24.50
Purchase #5	$50.66	13.187%	$57.3405	$57.34	$57.35	$57.30
Purchase #6	$219.56	11.333%	$244.4427	$244.44	$244.45	$244.40
Purchase #7	$201.59	10.812%	$223.3859	$223.39	$223.40	$223.40
7 purchase totals =	$1,126.31		$1,234.3361	$1,234.33	$1,234.35	$1,234.30