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	$28.95	11.295%	$32.2199	$32.22	$32.20	$32.20
Purchase #2	$37.94	6.244%	$40.309	$40.31	$40.30	$40.30
Purchase #3	$248.75	6.112%	$263.9536	$263.95	$263.95	$264.00
Purchase #4	$110.54	12.249%	$124.08	$124.08	$124.10	$124.10
Purchase #5	$237.74	11.792%	$265.7743	$265.77	$265.75	$265.80
Purchase #6	$74.74	5.649%	$78.9621	$78.96	$78.95	$79.00
Purchase #7	$128.73	10.686%	$142.4861	$142.49	$142.50	$142.50
7 purchase totals =	$867.39		$947.7850	$947.78	$947.75	$947.90