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	$36.34	5.388%	$38.298	$38.30	$38.30	$38.30
Purchase #2	$209.87	13.347%	$237.8813	$237.88	$237.90	$237.90
Purchase #3	$88.54	11.603%	$98.8133	$98.81	$98.80	$98.80
Purchase #4	$38.81	4.307%	$40.4815	$40.48	$40.50	$40.50
Purchase #5	$111.70	10.132%	$123.0174	$123.02	$123.00	$123.00
Purchase #6	$36.78	8.760%	$40.0019	$40.00	$40.00	$40.00
Purchase #7	$110.35	7.765%	$118.9187	$118.92	$118.90	$118.90
7 purchase totals =	$632.39		$697.4121	$697.41	$697.40	$697.40