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	$187.26	9.194%	$204.4767	$204.48	$204.50	$204.50
Purchase #2	$98.36	13.773%	$111.9071	$111.91	$111.90	$111.90
Purchase #3	$176.63	11.165%	$196.3507	$196.35	$196.35	$196.40
Purchase #4	$25.96	10.455%	$28.6741	$28.67	$28.65	$28.70
Purchase #5	$116.69	5.598%	$123.2223	$123.22	$123.20	$123.20
Purchase #6	$202.26	4.319%	$210.9956	$211.00	$211.00	$211.00
Purchase #7	$98.52	7.306%	$105.7179	$105.72	$105.70	$105.70
7 purchase totals =	$905.68		$981.3444	$981.35	$981.30	$981.40