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	$68.99	13.807%	$78.5154	$78.52	$78.50	$78.50
Purchase #2	$82.83	9.512%	$90.7088	$90.71	$90.70	$90.70
Purchase #3	$6.92	10.546%	$7.6498	$7.65	$7.65	$7.60
Purchase #4	$182.51	11.541%	$203.5735	$203.57	$203.55	$203.60
Purchase #5	$220.46	4.119%	$229.5407	$229.54	$229.55	$229.50
Purchase #6	$248.32	8.387%	$269.1466	$269.15	$269.15	$269.10
Purchase #7	$65.36	7.308%	$70.1365	$70.14	$70.15	$70.10
7 purchase totals =	$875.39		$949.2713	$949.28	$949.25	$949.10