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	$90.65	9.790%	$99.5246	$99.52	$99.50	$99.50
Purchase #2	$71.92	6.149%	$76.3424	$76.34	$76.35	$76.30
Purchase #3	$243.75	12.545%	$274.3284	$274.33	$274.35	$274.30
Purchase #4	$17.72	3.309%	$18.3064	$18.31	$18.30	$18.30
Purchase #5	$235.69	4.764%	$246.9183	$246.92	$246.90	$246.90
Purchase #6	$17.71	9.344%	$19.3648	$19.36	$19.35	$19.40
Purchase #7	$91.58	5.238%	$96.377	$96.38	$96.40	$96.40
7 purchase totals =	$769.02		$831.1619	$831.16	$831.15	$831.10