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	$222.30	4.862%	$233.1082	$233.11	$233.10	$233.10
Purchase #2	$171.36	8.447%	$185.8348	$185.83	$185.85	$185.80
Purchase #3	$68.83	11.605%	$76.8177	$76.82	$76.80	$76.80
Purchase #4	$177.29	11.870%	$198.3343	$198.33	$198.35	$198.30
Purchase #5	$198.36	11.341%	$220.856	$220.86	$220.85	$220.90
Purchase #6	$5.40	7.404%	$5.7998	$5.80	$5.80	$5.80
Purchase #7	$73.89	5.775%	$78.1571	$78.16	$78.15	$78.20
7 purchase totals =	$917.43		$998.9079	$998.91	$998.90	$998.90