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	$72.61	7.834%	$78.2983	$78.30	$78.30	$78.30
Purchase #2	$232.73	10.844%	$257.9672	$257.97	$257.95	$258.00
Purchase #3	$79.95	10.752%	$88.5462	$88.55	$88.55	$88.50
Purchase #4	$220.37	7.485%	$236.8647	$236.86	$236.85	$236.90
Purchase #5	$57.86	3.161%	$59.689	$59.69	$59.70	$59.70
Purchase #6	$159.47	10.579%	$176.3403	$176.34	$176.35	$176.30
Purchase #7	$207.46	5.650%	$219.1815	$219.18	$219.20	$219.20
7 purchase totals =	$1,030.45		$1,116.8872	$1,116.89	$1,116.90	$1,116.90