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	$7.87	13.258%	$8.9134	$8.91	$8.90	$8.90
Purchase #2	$99.58	9.595%	$109.1347	$109.13	$109.15	$109.10
Purchase #3	$82.32	3.654%	$85.328	$85.33	$85.35	$85.30
Purchase #4	$111.67	12.436%	$125.5573	$125.56	$125.55	$125.60
Purchase #5	$141.75	10.703%	$156.9215	$156.92	$156.90	$156.90
Purchase #6	$48.51	4.415%	$50.6517	$50.65	$50.65	$50.70
Purchase #7	$75.99	9.640%	$83.3154	$83.32	$83.30	$83.30
7 purchase totals =	$567.69		$619.8220	$619.82	$619.80	$619.80